-tells you how the music is counted in each measure and which note constitutes one beat.
How many beats per measure
which note is counted in the measure, in this case, quarter note is counted per beat.
So the only numbers you will see as the bottom number (the denominator) will correspond to note values:
2 half note
4 quarter note
8 eighth note
16 sixteenth note
You could continue on with 32, 64, but it does not appear often in music compositionon. The most common bottom numbers are 4, 8 and 16.
quarter note is counted as beat, and 3 beats are counted per measure.