How to block out part of the world from view

im trying to block out the view of the world, other than a certain spot. Im not too good at explaining, so heres a video of what im trying to accomplish (i guess you can say a “VR” style view)

anyone have any ideas on how i can go about this?

im well aware how to make GUI objects, thank you.

out of all due respect, did you read and take the time to understand the post, or just post something completely unrelated just to post a reply?