MIUI is pretty short on instructions so some of the following might be helpful – thanks to Team D1-MIUI for some of these

Dani (xavierjohn22) has written a very detailed manual Available on XDA

• Desktop & Launcher 
  • How do I change the desktop layout?
    To put widgets on desktop, long press on empty space on desktop, you’ll see two icons on either side of the rubbish bin – tap on them, drag & drop the widgets onto whichever desktop screen you want.  Drag icons to bin to get rid of them
  • How do I add more desktops?
    Press Home button twice, you can then add desktops.  You may add or move (drag and drop) screens. Not sure if there is a limit, but it may be 20 or so.  The last screen you were at before entering this mode will be highlighted.  The defaut home screen will have just the home button highlighted.  Just tap the little home button on the thumbnail to switch the default
  • How do I delete desktops?
    Press Home button twice, you can then remove desktops.  You may only remove empty (ie no icons) desktops (click the X in the top right corner)
  • How do I change transitions?
    Settings > Application > Launcher Settings & there should be a list at the bottom called “Select screen transition effects”
  • How do I move icons onto different screens?
    Long press on empty space on desktop, press and hold icon you want to move, then with your other hand scroll to a different screen and then release the icon
  • Launcher Dock
    Can be populated up to six shortcuts or folders by drag and drop.  Custom shortcuts (ie widgets) will not drop here
  • There’s no App Drawer!  Everything is on a desktop!
    This feels a bit strange after using Sense.  Create a folder for the stuff you don’t use and move all the icons into that folder.  You could even call the folder “App Drawer”.
  • Edit Mode (long press on screen, or select from MENU).
    This will allow you to customize your home pages.  While in edit mode pressing the MENU button will bring up the add button for custom shortcuts, widgets, folders, and wallpapers.  Widget dropdown and wallpaper options are also accessible via buttons in the upper right and left hand corners of the screen
  • Widgets
    One of the coolest things about this launcher is the ability to add all of your widgets in one session. Simply drag widget from dropdown menu to desired thumbnail screen, you may have to adjust on screen placement later. Then grab the next one and repeat until you are done, AWESOME.
  • Battery % Display
    Change Battery display options on Settings > System > Battery > Battery indicator style
• Lock screen
  • Wallpaper
    You may change the wallpaper for the lockscreen in the same menu as normal wallpaper, select lockscreen wallpaper gallery to pick image from your SD card. 
  • Notifications
    There are notification counters for Phone calls and Text messages.  Long pressing on the phone or texting icons will preview the missed calls or texts.  Unlocking with these icons will open directly to those apps.  For now the text notifications are tied to the MIUI MMS app. You must open the messages with that app to clear the notifications. The icon can be directed to handcent or other messaging app but notifications still come from MIUI MMS.  (Edit: At least one user is reporting using ChompMMS and has lockscreen notifications working)
  • Music Player
     Double tap the lock icon to access the music player when the phone is locked
  • Change which music app responds to lockscreen controls
    Settings > System > Hardware Key Settings > Default app to respond to Media key
• Notification Pulldown
  • What’s all those icons at the bottom of the notifications pull-down?
    You can do lots of common tasks by clicking the icons at the bottom of the notification blind.
  • Press and hold down an icon at the bottom of the notification pull-down
    Opens the settings for that icon.
  • What does the CPU icon do?
    Unlit= default or max set CPU,  Lit= -200 Mhz (maybe – there are lots of theories about what this icon does normal maybe 200Mhz overclocked and lit=some sort of battery saving by dropping MaxCPU by 200Mhz)
  • What does the APN icon do?
    It toggles 3G/HSDPA (unlit=2G mode)
• MIUI Music
  • How do I backup MIUI Music playlists?
    On a song or any screen in MIUI Music player, bring up the tab or blinds (whatever it is called), Press Menu, now you can add to playlist, edit the playlist etc..
• Dialer
  • Dialer seems limited compared to what I am used to
    Yes it is, but it is getting better with each update - suggest install DialerOne from the market.  Move the stock Dialer icon to a folder on another desktop and put DialerOne icon on the home desktop or launch bar.  DialerOne also has very good smart dial.
  • Is it just me or is there no option to create speed dials with this ROM?
    There are no speed dials on the stock dialer, but there are on DialerOne. If you backup DialerOne with Titanium and restore from Titanium after a ROM upgrade all your speed dials will also be restored.
• Gmail
  • How do I get an unread message count on Gmail?
    Get Gmail Unread Count from the market, then move the stock Gmail icon to a folder on another desktop and put this icon on the home desktop.  Unfortunately you can’t put it on the launch bar because its a widget.
• SMS
  • SMS seems to have limitations, no vibrate, no repeat for missed SMS
    Install HandCent from the market, turn off standard messaging notifications and turn on Handcent SMS notifications.  Move the stock Messaging icon to a folder on another desktop and put Handcent icon on the home desktop or launch bar. 
    Update 0.12.3: SMS now has vibrate option, but still no missed notification.
• File Manager
  • If you are in file manager, and you swipe a file sideways, the delete icon will automatically appear in place of the check box, allowing you to delete it by itself
  • Long press on any file brings up Copy/Move/Send/Delete etc
• Contacts
  • Custom Ringtones
    You may select custom ringtones for each contact if desired. 
  • Custom Picture
    If you select to assign a picture to a contact, a list of almost 100 “recommended” contact pictures comes up, everything from flowers to video game characters.  Buttons to take a pic and select from sd card are in the lower corners.
  • Delete
    Swiping across a contact in the list will give an option to Delete.
  • Favourites
    In order to use the Favorite contact widget that is included you need to add favorite contacts by pressing add to favorites button when you open the contact.
  • Replacement App?
    Youlu (look for it on Appbrain) is a very good replacement for the stock contacts app.  Only annoyance is that stupid thing force closes if you get a call from someone without callerid.
• Other Controls
  • How can I silence the phone when it is ringing
    Turn it face down (Settings > Sound > Flip to Silence)
  • Home then Menu or press and hold Home
    brings up list of recently used apps plus AppKiller and AppManager.  Swipe to the right, and a new window will appear for Global Search
  • How do I take a Screen Shot?
    Hold Menu then Vol Down –  then look in gallery.  Miui will create a folder on your sd card called MIUI.  This is where your screen shots will be saved.
  • Is there a way of making the optical tackball button wake up the phone?
    Settings -> System -> Button Settings -> Trackball wake
  • Return to call button
    You can leave the call screen to do other tasks, including browsing the web (WiFi only), during a call.
    When you leave the call screen a button appears across the top of your screen that will return to the call screen so you can hang up.
• General
  • Why does bluetooth have to be on for the FM radio to work?
    This is part of the HTC hardware design.  It happens in the stock Desire ROM automaticcally and doesn’t display the Bluetooth icon.
  • Please can I have a horizontal slide to unlock?
    Sure – buy an iPhone or use TME, but its not available in MIUI ATM.  MIUI vertical unlock is much less error prone than stock HTC
  • How do I switch to Disk Drive mode?
    Select on popup after connecting USB.  Change by clicking the message on the notification blind.
  • Uninstalling Apps
    Since there is no app drawer, when you drag a shortcut to the trash can it is going to ask if you would like to uninstall.  You can also uninstall using Settings > Programs > Manage Applications.  You may not uninstall system apps in this manner
  • Transferring Files by FTP
    Attach to Wifi, then FileManager > Network > Start Service
    Then just use filezilla or whatever to connect to the ip and port (2121) shown.