Martingale is definitely one of the most widely known and most successful roulette strategies (for some it is the best roulette strategy), and it is very simple to apply. It can be used only for outside bets, those that provide almost 50% chance of winning, and excluding the 0.
Say a single-number bet has a 35:1 payout, and you betR$1. If you win, you'll get your money back plusR$35. Another example: If you win aR$100 bet (for a 35:1 payout), you get a total of $3,600 ($3,500 profit plus theR$100 you initially bet).