Odd / Impair: an odd number. Low bet / Manque: numbers 1 - 18 (Manque is French for "failed" and is used because the ball has failed to pass 18) High bet / Passe: numbers 19 - 36 (Passe is so named because it has "passed" the centrepoint)
To win at roulette, watch the wheel spin a few times before placing your bet. If you see any pattern, such as a high frequency of obstacles, you can use it to influence your bet. If you are given a choice between European and American roulette, choose Europe, which offers a slightly higher chance of winning.