I start yoga exercise for weight lose. Instructor said it is not for that. Is there something better so that if I leave yoga I wont gain?

Aerobic Exercise. Yoga is a great way to gain strength, flexibility, focus and many other great benefits. That siad, if you want your focus to be weight loss, you need to burn calories. Aerobic exercise is the way to go: walking, running, bicking, etc. The key is to achieve a pulse about 60% of your maximum (220 - age). Shoot for about 30 to 45minutes a day but always start slow if your not used to exercise.