Cool. Which ones are you looking at?
Alright, so the SAT is split up into a few sections: Math (verrrryyy easy hardly even GCSE level), Critical Reading (Can be tricky with time constraints but still straight forward) and Verbal/Writing.
Usually you have between 20-25 minutes to answer a set of questions, there are about three of these per section. The total time you'll be taking the exam for is ~3.5 hours give or take a few breaks.
For revision, get the massive '
blue book' Learn the techniques and do tonnes of practice papers.
I suggest doing the SAT in Yr 12 (preferably in the beginning). This allows as much time as possible to retake.
If you're applying to top unis like the Ivies + MIT, Stanford etc. Then you'll need to do subject tests. These should probably be based on what you'll be studying at A-level. 3 is the recommended amount you should do.
If you have anymore questions fire away!