When you listen to music, you can hear a regular beat. Beats
are organized in groups of the same number and these are
called bars. The first beat of a bar is always stronger than the
rest. If the strong beat comes every 3 beats, then the music you
are listening to has three beats in every bar.
In written music, bars are separated by bar-lines. At the end
of the composition, a double bar-line is used to show the end.
There is always a time signature at the beginning of the piece.
It goes to the right of the clef. It’s written using two numbers.