If you put appropriate percentage of your portfolio into stocks, bonds, real estate, and cash savings you'll probably do fine. Each is better suited to some goals and time horizons than others. Bond funds are designed to provide a stream of income. The income is typically derived from interest paid on the maturing bonds. Both your principal and rate of interest will change in value.
Stock funds are subject to dramatic short term price fluctuations.
However, stocks have grown fast enough to outpace inflation, and money market and bond investments. The secret of a successful investment strategy is selecting investments whose risk and reward characteristics fit your financial goals and time frame, and to stick with them. In selecting stock, if that interests you, consider the products you use regularly. Most people seem to think that you need to invest in the cutting-edge technology stocks for big returns, but if you don't feel comfortable investing in that market, look at the daily use products. They provide products you use every day to bathe, brush your teeth and wash your clothes.