Don't worry, it's not hard at all. :) Let me break it down for you:
The Color Scheme Designer will give you a series of complimentary, secondary, or mono colors. Go to the top bar on the page, and click on "Random" (it's next to color blind and redo). Keep shuffling the randomizer until you settle on a scheme you like. Next, in the same bar as "random", click on Export > HTML + CSS. This will open up a new window with the hex codes of each color.
The next thing you want to do is insert those hexes into your profile. When you customize your profile, it has different fields for where to insert the hexes. So, underneath the "text color" field is "background color". This is where you should apply one of the hexes from the scheme you like.
The best thing you can do is experiment, because there's no right or wrong way to design a profile. As long as the text is readable, you're good to go! :) So just play around. Lastly, only supporters and staff are allowed to insert images into the profile, so unfortunately you're going to need to donate to PC if you want to start playing around with that sort of stuff. But that doesn't subtract from how fun designing a profile can still be!
That link will help you organize colors and pick the best scheme for you regarding your tastes. I use this all the time and it's really a great resource. I can guarantee you'll find a series of schemes that can really make your profile special. n_n;