The time signature affects how you interpret the notes that are written.
The two numbers at the start of music represent how it is read and how much space is in each measure. Bottom note is the kind of note that gets one beat, 4=quarter, 8=eight, 2=half, etc. Top note is the number of beats in a measure.
4/4 means quarter notes gets one beat and there are four beats in a measure.
“Common time” is another way of saying 4/4.
It looks like this:
3/4 is the same as 4/4 except that there is one less beat. Try imagining that it’s in 4/4 at first, but the grouping is a little different, groups of three or six instead of four or eight for quarter notes/eighths.
2/2 is known as ‘cut time’. It means a half note gets one beat and there are two beats in a measure. Therefore, music that looks the same but has the 2/2 time signature will be interpreted in a different way.
Most of the time you will see 4/4 time.
Notes & Rests
In 4/4 time, each measure has four beats and a quarter note gets one beat or count.
Whole note or rest: 4 counts
Half note or rest: 2 counts
Quarter note or rest: 1 count
Eighth note or rest: 1/2 count
Sixteenth note: 1/4 count
Eighth notes and sixteenth notes can be written with ‘beams’ which are the horizontal lines connecting the notes or ‘flags’. You see beams more often when multiple eighth or sixteenth notes are connected and flags more often when they are isolated.
Flags look like these: