Use this chart as a reference guide for Sit-n-go play. As your game progress's you'll be able to make adjustments based upon your experience level. This chart is a great place to begin. Remember, the strategy for hand selection in single table sit-n-go's is completely different than cash games or multi-table tournaments. As a beginner, it is highly recomended to stick with STT's until your game improves.
Mr. Blackjack gives a very easy to understand tutorial video on what beats what in Texas Hold'em poker.