Hi Greg,

In simple meters, the bottom note will get the beat, and the top will be how many notes are in the measure.

Example:

3/4=3 quarter notes per measure, Quarter note gets the beat
4/4= 4 quarter notes per measure, Quarter note gets the beat
3/8=3 eighth notes per measure, Eighth note gets the beat

Compund meter is a little different though..Here are a couple links that could help.

http://www.teoria.com/reference/reading/12.htm
http://www.teoria.com/reference/reading/18.htm

Good Luck