Initially if you are a complete novice, tighten the wheels of your skate so that they don't roll. Walk around with them for a couple of hours (spread over a few days) while you get used to the weight. Loosen your wheels as you grow in confidence.
As you start rolling, when you put a foot forward, Newton's third law might send your rear leg back. Try to skate with your legs in a small 'V', so that the rear leg don't completely roll away Happy skating