I had a hard time figuring out how to do this myself so i decided to help others with this process. After done you figure out it wasn't a hard thing to do. (sorry about pictures, my camera is broken and I had to use my computers built in camera).
Step 1: Get a usb to mini usb cable
This is the crucial part in this process, without this you can't do anything I'm going to show you. So if you have one continue, if you don't go out and buy one. Also if you are lucky enough to own a playstation 3, like me, you can use the same cable you charge the controllers with.
Step 2: Connect psp to computer
Connect the usb to mini usb cable. the usb goes into you computer and the mini usb goes inside the psp. The imput is located on the top of the psp right in the middle. After that go into your psp and go into "settings", then "USB Connection". Once done you should get a message on your psp saying "USB Mode". Then you should get a message on you computer asking what you want to do. Click on "Open folder to view files" or something similar depending on your operating system. If you do not get this message go into "My Computer" and find the psp. You should get a screen that has "MP_ROOT" and "psp"
Step 3: Themes, Pictures, Music, and games
For Themes go into "psp" then right-click select "new" then "folder". Name the new folder "THEME", It HAS to be in all caps. My favorite site for themes PSP Themes
.Now do that again for pictures naming the folder "PHOTO". For Music name the folder "MUSIC" and for games name it "GAMES" or "GAME" it depends.