An infinitely small location in space marked by a specific coordinate. A point has no length, width, or thickness. No matter how closely you look, a point is still just a point.
A line is a collection of points extending along one dimension. Since points are infinitely small, a line consists of infinitely many points. Strictly speaking, a line is also infinitely long and extends forever in either direction.
A line segment is what we think of as a line. It is really a part of a line with a certain length. It consists of all the points between a beginning and an ending point.
A ray is a hybrid of a line and a line segment. It has a beginning point, but it extends out to infinity in one direction.
A plane is a two-dimensional sheet defined by any three points. It is like a sheet of paper that extends out to infinity in both directions.