Just wondering if there is any site or volunteering forum where I can select small time job from other non-artists to do basic works. I don’t really want to be involved with big projects but if someone need a simple banner or some simple photo editing and whatnot, those are the kinds of works I would like to try my hand on. I would like to develops my skill but I have never really done well working purely for myself. I do better learning and applying my skills if it is for others. Hope that my explanation is clear enough. Thanks 
You live in D.C. There are bound to be some non-profits near by who would love to have some free graphics work. Think of what causes you support, find an office and contact them.
You could even go down the local Occupy DC encampment at Mc Pherson Square and see if they need anything for signs, handbills or web work. Here’s their website with contact information so you can even get in touch and stay at home.
http://www.crazedlist.org/ Allows you to search every craigslist city in the world with one query. I have found quite a few small jobs, and several large ones. Search in the “gigs” section.
Keep in mind most of the ads want something for free, but I have averaged about $10k a year from freelance on craig’s list. I have about a 1/50 success rate on finding freelance jobs. I have a form letter I send to every job link I find that looks interesting. It basically says "Hi, here is my reel, here are people I have done work for, contact info…