The command Distance(p1, p2) computes the distance between the points p1 and p2, which must have the same dimensionality (and orientation, when each of the points is a Vector).

This command is part of the Student[Precalculus] package, so it can be used in the form Distance(..) only after executing the command with(Student[Precalculus]).  However, it can always be used in the form Student[Precalculus][Distance](..).