A stop-loss order is designed to limit losses on a position in a security. For long positions, a stop loss can be placed below a recent low, or for short positions, above a recent high. It can also be based on volatility. For example, if a stock price is moving about $0.05 a minute, then you may place a stop loss $0.15 away from your entry to give the price some space to fluctuate before it moves in your anticipated direction.
You're probably looking for deals and low prices, but stay away from penny stocks. These stocks are often illiquid, and chances of hitting a jackpot are often bleak. Many stocks trading under $5 a share become de-listed from major stock exchanges and are only tradable over-the-counter (OTC). Unless you see a real opportunity and have done your research, stay clear of these.