I think the easiest way to tackle these questions is to plot the vertices and look at the shape. You'll quickly see whether the given vertices form a rectangle - or something else entirely!
Each of those letters corresponds to a point on a graph. Do you know how to plot points? If you mark each of those vertices on a graph, you should see whether they form a rectangle. By the way, do you know what a vertex is? In this case, they correspond to a corner of the rectangle.
If you don't know how to plot points, the problem is a little more difficult. You'll have to use your knowledge of the properties of a rectangle, e.g., that its opposite sides are parallel, that each angle has 90 degrees, and so on. It's possible to determine whether BG and HL are parallel, or whether BL and GH are, just from the points. But it's a lot more work than looking at the graph.
Let me know if you need more hints.