In perspective drawing,
every set of parallel lines has its own vanishing point. When viewing things in TWO POINT perspective, we are viewing the object or scene so that we are looking at one corner, with two sets of parallel lines are moving away from us. (The remaining set of parallel lines, the verticals, are still straight up-and-down we only worry about those when we're doing three-point perspective!).
It sounds confusing written out like that. But the way it looks - as in the picture above - is familiar, and if you follow the steps, you'll find it easy to draw two point perspective. Just remember: the verticals stay straight up and down, while we 'vanish' the left and right sides towards a vanishing point.