A displacement vector is just a way of representing a change in position. It's an arrow that points from a starting location to an ending location.
For example, if a person is walking on a flat surface that we have (mentally) imposed a rectangular coordinate system on, and if the person starts at the point whose rectangular coordinates are
The so-called "components" of the displacement vector are the differences of the corresponding coordinates:
The person does not have to walk in a straight line, but the displacement vector itself is straight.