I know a few people have complained of ScriptSmart being difficult to use (I did originally too) so here's how I do things in the hope that it helps at least one other person. Remember it's free, so worth persevering with!
Go to the ScriptSmart page on the Writers' Room website at http://www.bbc.co.uk/writersroom/ and select downloads (or just go to http://www.bbc.co.uk/writersroom/scriptsmart/downloads.shtml)
Download ScriptSmart Gold (as it comes with a menu for whichever type of script you're writing ie radio, tv sitcom, tv drama, etc) and unzip the file. Chances are it'll stick it in c:\windows\application data\microsoft\templates\Script Smart (as that's where it's just put it for me!).
Double-click on "ScriptSmartGold2.dot" in the above folder, 'enable' the macros when prompted by the box and you should get an information message about
'Script Smart Gold (Version 2.9) created by Matthew Carless...'
Click 'Yes' and then you'll get a menu asking what type of script you want to write: Film, TV Drama, TV Sitcom, Radio, Radio sketch, Stage, Comic Book.
Pick one of them and it'll ask you for the title. Do this and click OK. Click 'Yes/No' if you want scene numbers and you're in and ready to work. (At this point I'd 'Save As...' so you're not overwriting the document template)
There is a toolbar at the top with stuff like a clapperboard and footprints on it; this is the control toolbar for F/X, action, new scenes, new character for dialogue, end the scene, etc, etc. Play with this first as you need to get to grips with it. The 'Return/Enter' key moves from character to dialogue in the easiest way (I find) and pressing tab puts in brackets for descriptions whilst talking. 'Tab' once more takes you back to the text again. 'Enter/Return' will go back from dialogue to character name and vice-versa.
Hope this is helpful.
Dan