The first thing you need to know is that in perspective drawing, every set of parallel lines has its own vanishing point. That will make more sense in a moment. Remember from math class that parallel means running side by side, the same distance apart. So, the sides of a road or the sides of a door can both be thought of as pairs of parallel lines.
Let's look at this picture. It shows a one-point perspective view. All of the lines that are parallel to the horizon (at right-angles to the direction of our gaze) such as the railway sleepers and fence posts - go straight across or straight up and down. If they were longer, they'd keep going straight across, or straight up and down, staying the same distance apart and not meeting.
In constrast, the lines moving away from us appear to get closer together as they get more distant, and meet at a vanishing point in the middle distance of the picture.
To draw one-point perspective, we arrange our view of the subject so that one set of visible lines has a vanishing point right in front of us, and the set at right-angles goes out to infinity on each side. So if it's a road, it goes straight away from us, or if it is a house, one wall goes straight across in front of us, not sloping. In reality of course, there are always objects which won't be lined up perfectly, but for now, let's keep things simple!