I'm still learning, I use limit for buying and selling.
Here's a detailed
explaination from Scottrade:
Limit Order - Order to buy or sell a stated amount of stock at a specified price or better.
Market Order - Order to buy or sell a security at the best available price. Most orders executed on the exchanges are market orders.
Stop Limit Order - An order to buy or sell at a specified price or better (called the stop-limit price) but only after a given stop price has been reached or passed. For example, an order to buy 100 MSFT 55 Stop 56 Limit, means that if the market price reaches 55 (stop price) or better (in the case of a buy, it would be less than 55) the order is then triggered to execute the order as a limit order at 56 or a better (lower) price. Stop-limit orders avoid some of the risk a stop order has, but like all limit orders, carries the risk of missing the market all together, since the specified limit price or better may never occur.
Stop Order - A stop order is an order to buy or sell a stock once the price of the stock reaches a specified price, known as the stop price. When the specified price is reached, your stop order becomes a market order.
