As you may infer from this question, I'm a complete noob. I've gone through quite a few tutorial videos but I still don't understand how I can create this shape...
You can do this by modifying a simple plane.
Add a plane: Shift A -> Mesh -> Plane
Go into edit mode: Tab
Go into vertices mode: Ctrl Tab -> 1
Select all vertices: A
Bevel vertices: Ctrl Shift B
This will create an ngon, ideally we would only like quads (faces with only four vertices)
If you want to fix this you can easily connect two vertices.
Select two opposing vertices and connect them by J
Repeat until all ngons are gone