First, the horizon, which gives the illusion that the picture is showing a big space.
Second, is the vanishing point, the vanishing point is somewhere on the horizon line, doesn't always have to be in the middle. the vanishing point defines where in you drawing, to put less detail. like in real life when you see something tall far away, but you can't see every detail on it because it's far away. it's the same thing with a drawing.
the vanishing point tells you, when the subject is closer to the vanishing point, that's when it tells you to make things small and add less detail.
and then there's the subject that points from the front to the vanishing point. usually, a linear object like a road or train tracks.
the outcome that occurs when using this technique makes your drawing or painting look like it's in a big space, or world instead of a small room, or inside a box.
Here's an image that should help you with that