A stockbroker is someone that buys and sells stocks on behalf of clients. While this only revolved around stocks of companies previously, stockbrokers nowadays cover a wide variety of asset classes.
There are various kinds of brokerages and brokerage accounts. Traditionally, stockbrokers used to double as investment advisors. Not only would they perform the trades for their clients, but they would also guide them on what to purchase.
Nowadays, the advent of discount brokerages has changed all that. Many stockbrokers no longer offer investment advice. Instead, they just execute the trades on behalf of their clients.
Another huge shift that has occurred is the switch to online trading. Instead of placing your orders by phone, you can now trade instantly through your computer. The automation of the trading process has led to some of the lowest trading fees in history.