Here's some tips.
Downlaod GIMP, it's free and a simple version of Photoshop.
Save your graphics as .png for best quality.
Download textures and PNGS to add some detail so it's not just a picture on a background with text.
Use the fuzzy selection tool or the fuzzy brush to remove a background from the model you want to use.
Look for some tutorials to help you improve.
There's other stuff but it would take me all day to explain ok.