Hi, what is the use of the other 4 points that are created with the vanishing point? I've noticed that if I move one of them the vanishing point changes its position but I've not understood very much.
Thanks in advance

Those four dots are two pairs of dots. Each pair forms a thick grey line and the intersection of those lines defines the location of the vanishing point.

You can move the vanishing point to where you want it by dragging it or you can use the dots to define the vanishing point based on reference points in an image.
This would be useful if you have a perspective sketch or a photograph of buildings that you want to work with. You'd place the dots on a face of a building (e.g. the roof line and a lower floor window line) and this would automatically put the vanishing point in the correct position.

Thank you very much