Interest can be paid periodically during the life of the debt or at maturity, depending upon the type of bond. At the end of that time, the issuer promises to repay the amount of the bond. The amount of risk is also related to the length of maturity of the bonds. Although there are no penalties for selling a bond before the end of its term, the value of the bond is subject to the current interest rate. If interest rates have risen since you bought your bond and you have to sell it, you may receive less than you paid for it.
Stocks represent an ownership interest in a company in the form of shares.
In buying stocks, you're looking for a company that will perform well in the future so that the value of your stock will increase. Some stocks also pay investors a portion of their earnings in the form of a dividend. Buying stocks is for the educated, savvy investor not for the squeamish. At best, picking stocks is an educated guess, and you take all the risk. If the stock price does go up as you anticipated, you can sell your stock for a profit.