When you buy or sell a security, you generally do so through a brokerage firm. Brokerage firms fall into two main camps: full-service brokers and discount brokers. Discount brokers charge far lower commissions than full-service brokers, and a growing number of deep discounters charge especially low commissions. But there is a trade-off. If you use a discount broker, you will get little or no investment advice, so you must be willing to make your own buy and sell decisions. A full-service broker, on the other hand, will help you pick investments and devise a financial plan.