Here is a tutorial on filters within Photoshop. The filters are a great set of tools for experimentation. They will allow you to produce a wide range of aesthetic effects. Changing the appearance of your photographs, layers, or selections.
If you don't feel like reading the article, here are the essentials:
1. Open a photograph in Photoshop. [File->Open]
2. Find and open your filter gallery. [Filter->Filter Gallery]
Now, browse through the various filters and have fun! Remember, you will be able to preview everything before you apply it to your photograph and Ctrl+Z/Cmd+Z will undo the effects you apply.