Great, I love seeing people who think like me. I am 22 right now but I had your mindset at your age. I would get a summer job and have a chunk of money and didn't know what to do with it. Now, keep in mind this was before Yahoo! Answers was around but I did ask others and this was the answer I received.
I would suggest shopping around different banks in your area and note what rates they are offering on their Certificates of Deposit (CDs). With a CD you agree to give your money to the bank for a fixed amount of time and the longer you give it to them the higher interest rate you will achieve.
Next, come up with a time period you want this CD to mature (ready for you to get your money back without penalty). I set my date for the summer after I graduated college which will be August 2007. I picked that date because I'll have finished a stage or chapter of my life, college, and could reevaluate my situation and see what I wanted to do with the money at that point in my life such as get a car, down payment for house, reinvest.
Now for the monthly amount you wish to contribute, contribute that to a savings account. You'll be getting a little interest and can still get to your money if there is an emergency. When you've saved up another chunk of money 500, 1,000, 1,500 open another CD that will mature around the same time as the previous CD. Mine was easy to set up because I would open CDs in August after my summer jobs or February after working for winter break. Since those months are 6 months apart it worked perfectly that banks have CDs for 6 and 18 months too.
You don't want anything too risky when you're young and CDs provide a safe environment for your money to get a decent return.
Hope this helps,
Glen