There are many types and styles of mutual funds. There are stock funds, bond funds, money market funds, and balanced funds -- to name a few.
Mutual funds allow you to invest in the market whether you believe in active portfolio management (actively managed funds) or you prefer to buy a segment of the market with no interference from a manager (passive funds and index funds). The availability of different types of funds allows you to build a diversified portfolio at low cost and without much difficulty.
The Variety of Fixed Income Mutual Funds
If you decide that you should own bonds as a portion of your portfolio, then you have many options. You can buy individual bonds or bond (fixed income) mutual funds. The variety of mutual funds that own bonds range from high-yield bond funds to money market funds.