Investing in bond funds is different from individual bonds. When you invest in a bond, you lend the issuer money. The issuer then pays you regular interest for the duration of the bond and repays the principal at the bond's maturity date, provided the issuer does not default.
A bond fund is a mutual fund that comprises many bonds, with a professional fund manager who buys and sells securities to keep the fund true to its specific investment objective. A bond is a debt security, similar to an IOU. Bonds can serve as an attractive "middle ground" between stability (cash) investments and stocks, offering investors the potential for more meaningful returns than cash investments - with less overall volatility than stocks.
An appropriate asset mix is essential to your long-term investment success. Although diversification cannot protect against loss in a declining market or assure a profit, a diversified portfolio should be less volatile than one that's invested in just stocks. That's because the underperformance of one type of investment may be offset by the strong performance of another.