The time signature consists of two values, the upper and lower value.
The upper value indicates the number of beats per measure.
The lower value indicates which note gets one beat.
In the example below a 3/4 time signature is used, where we have three beats to the measure.
The most common time signature is 4/4 and in the music notation this is often indicated by the letter C instead of 4/4.
When a song is long, for example you need 3 staves, only the first stave has the clef symbol and the time signature. The other staves have only the clef symbol.