Their are several site that can show you how to make them,

these 2 listed below are were i started.

Tutorals to get you started.

1.
MS Paint (this you will find on your computer under the Start/Programs/Accessories/Paint)

2. Paint Shop Pro

these nest two are for photoshop,

3.
Potoshop #1 - this has upto 40 tips on using it

4.
Photoshop #2 - this one give tuts and lessons