Here you can learn how to read music.
Free music theory lessons online.

This site is for UK music terms.
If you want to learn American (US) music terms, then go to:
http://www.music4musicians.com/minute_a_day_music_theory.htm

We have learned about crotchets.

2 measures 4/4

Notes that are twice as fast as crotchets are called quavers.

One quaver is written like this.

eighth note or quaver

When many quavers are written together, they look like this.

Click the play arrow twice.
Listen to the difference between this (2 bars of quavers) and 2 bars of crotchets.

2 measures 4/4
Click the play arrow twice.