With a front-end sales load you pay the commission out of your initial investment. A back-end sales load charges the commission when you sell your shares. A level-load is a sales charge that is paid over several years of your investment. There are also no-load funds which some mutual fund companies sell directly to the public with no sales charge. These fees cover the fund's management, trading, marketing and administrative expenses.
Fees are often higher for funds whose management is more complex than they are for more basic funds.
For instance, international funds usually have higher fees than money market funds. Each fund's fees are detailed in its prospectus. It's a good idea to do some homework. You can contact any mutual fund company and ask for information on their funds and mutual fund investing in general. You can also select an investment professional to help you draft an investment plan that suits your needs.