Music is broken up into measures. A measure is a group of beats which ends with a line. For example, the picture shows us a rhythm with 4 measures. The measures have been labelled: 1, 2, 3 and 4. Can you spot the measures?
A time signature is a sign that tells us the number of beats per measure. If you look at the rhythm, you can count 2 beats in every measure. We add a time signature at the beginning to tell us how many beats belong in each measure. The highlighted section in this picture is the time signature.