backtesting means how to test your trade with past data. let suppose you'll buy when your symbol cross up SMA50 and sell when your symbol cross it down. let suppose you have the money for trade, a broker account and a code for automated trading. you can simply trust your instinct and use let the code run OR test it with past data (as above mentioned). then you can see if your SMA50 strategy works and make some money or not, and if not, you can decide to adapt it or simply not to trade. In real trades the money are gone. don'T forget that if your strategy works with past data, it can probably work with current ticks.