Have a look at the top right of the keyboard. There are three lights. One is Num Lock, one is Caps Lock and one is Scroll Lock.
For example, when you want to type in capitals you press the Caps Lock key and the Caps Lock light comes on.
Find the key which says NumLk on it. It is in the top right area of the keyboard. You will probably find that this key has two things on it, and NumLk is at the top. This means you have to hold down shift and press this key.
The Num Lock light will now go off.