Fail to see immediate threat

I only played casual chess before.  At the beginning of this year, I started to learn with Chessmaster.  I still haven't learned any openings because I'm not sure where to start.  I know I like to play e4 as white, and as black if my opponent plays e4, I like to respond with c5; the Sicilian.  my knowledge of openings end right there.  Where does a beginner start when learning openings other than basic ideas like move each piece once, push a center pawn forward, and try to castle short?  the only way I am learning right now is by experience.  I have to remember to watch out for my opponents' knight and queen fighting together.  they work great together because one piece can do what the other can't.  the knight can jump over pieces and attacks in a not so easy to see pattern.