Save the PSP file as the car_name.psp first so you can go back and make changes to it without having to paint the whole thing again...

Now save as car_name.tga and save it to your exports and imports folder inside the game.

Now go into the opponent manager and click the NEW button over on the right, select the make, name it and click the import button on the bottom right and find your paint scheme. Now save it.

Go into your player info screen and select the new car and go drive it!

That's how we all started... just hang in there, and don't hesitate to ask questions over at Racin Grafix... we all help new guys that want to learn.