You should see some tabs open near the top of the screen. Left click a tab to open it.
If the edit you see is OK, then middle click the tab to load a new edit. (if you don't have a 3 button mouse, then double click will also work)
If the edit is not OK, then right click the tab to revert it.
Once you have reverted an edit, you will be shown a form for selecting user warnings. Choose the appropriate warning and click 'warn'.
Once this has been completed, another edit will load. Repeat from the beginning until tired.
Other info
The coloured bar at the bottom of the screen will go grey each time you load a new edit. After MWT checks the block log of the user, it will either go green (if the user has never been blocked) or orange (if the user has items in his/her block log).
The coloured globe to the left of the address bar is usually green. It is in this state when the recent changes parser is idling. It goes orange while it is seeking new edits for reviewing, and red if there are no edits left to review. If at any time you feel the edits you are getting are out of date, you can double click the globe to reload recent changes.
See Wikipedia:MWT for more general information. (where you can put feature requests or bug reports)
If your question isn't answered here, then you can either log on to #mwt on irc.freenode.net, or for non-IRC users, simply leave a message on my talk page.
