Stocks are a gamble. You are buying into a company with hopes that they succeed. If they do eventually profit and pay off debt, then they may pay out the share (stock) holders. Bonds are a great investment as you are buying the companies debt. So you would then be the first person to get paid before the share holders when the company succeeds. If the company fails, you get nothing. and if you then have that bond, you are responsible for the debt. The stocks would have just cost you the initial investment. CDs are like savings accounts, or more comparable to a 401K. You put money in, it has interest earned over time.
Check out Sharebuilder.com for Savings accounts that have interest as well as being able to buy stocks and bonds.