Any beginners' music book will give you this info. Here goes...
On the stave, the bottom line is an E. The next four lines are G, B, D and F, and this can be remembered by "Every Good Boy Desesrves Fruit."
The spaces in between (reading from the bottom upwards) spell FACE.
Now, if you went BELOW the main stave to where the next line would be, ie one space (which would be D) and then to the next line this note would be C, actually Middle C which is the C in the middle of a piano keyboard. Now you can work out the other notes.
If you don't know which note is C, this is how you work it out. Look at the black keys (Sharps/flats) and you will see they come in twos and threes. Wherever you have TWO black keys together, the key to the left of the pair is C. The notes I've already mentioned above (C through to F) are the white keys to the right of this C. The keys repeat themselves all the way up the keyboard from C to B. Hope this is clear!