The Time Signature is the two numbers after the clef symbol. If there are no numbers then 4/4 is used and is known as common time.  The 4/4 time signature can also be represented with large C as well.

The top number represents the number of beats per measure.
The bottom number represents what note receives one beat.

2/4 means two beats per bar and the quarter note get one beat.
3/4 means three beats per bar and the quarter note get one beat.
4/4 means four beats per bar and the quarter note get one beat.

 

6/8 means six beats per measure and an eighth note gets one beat.
12/8 means 12 beats per measure and an eighth note gets one beat.

A time signature of 4/4 a quarter note is counted as 1 beat with four note per measure.
A time signature of 6/8 a eighth note is counted as 1 beat with with 6 notes per measure.