Time signatures show how many beats are in a measure and what type of note receives the beat (lasts for one beat).
In simple time: = 2 beats per measure; quarter note receives the beat
= 3 beats per measure; quarter note receives the beat
= 4 beats per measure; quarter note receives the beat
= 2 beats per measure; half note receives the beat
= 3 beats per measure; half note receives the beat
= 3 beats per measure; eighth note receives the beat
= 6 beats per measure; eighth note receives the beat
= 9 beats per measure; eighth note receives the beat
= 12 beats per measure; eighth note receives the beat
To review Meter and Measures see Understanding Meter.