At the start of the music you will see a time signature, this tells us how many beats are in each bar.

2
4        means there are 2 beats in each bar

3
4        means there are 3 beats in each bar

4
4         means there are 4 beats in each bar

Because 4 beats in a bar is one of the most common time signatures sometimes you will just see the letter C instead.

This is a semibreve and it lasts for 4 beats.

Next to it is the semibreve rest which also lasts for 4 beats.

The next note is called a minim and this lasts for 2 beats.

Next to it is a minim rest which sits on the middle line and is also 2 beats long.

The last note we will look at is called the crotchet and it lasts for 1 beat.

The squiggle next to the note is a crotchet rest and it also lasts for 1 beat.

All music uses any combination of notes and rests as long as each bar adds up to the correct number of beats (which you find out in the time signature).  In this case each bar must add up to 4. Check it and see!