Linear perspective techniques are used by artists to give the illusion of distance and space to drawings and paintings. One-, two-, and three-point perspective all refer to the number of vanishing points in each category. One-point perspective involves a single vanishing point and the most common example of it is two parallel train tracks that appear to merge at a single vanishing point in the distance. Two-point perspective allows for the illusion of corners, and three-point perspective that you are seeing objects from above or below.
For more, here's our perspective drawing resource guide.