Question / Help Screen Capture?

[quarkrad]

Apologies - newbie. I have 25.0.3 obs Studio running on ubuntu and have spent hours trying to work out (if?) how to select a specific area of the screen to record. If I am playing a video via my browser I'm trying to find out how to select a specific area of the screen to capture. I keep reading about using the Alt key but there is no detail on how to actually narrow down to the area you want. I get the impression obs is more suited to whole desktop streaming rather than used as a simple screen capture tool - but then I guess I don't know enough. Any help/suggestions would most appreciated.

 

[quarkrad]

So I have managed to capture a specific area of the screen by pressing Alt and the Windows keys together and then dragging the blue lines to the area I want. However, the recording shows the original screen size in black with the area I selected playing the video. Half way there - I just want the selected area recorded - not that area on a black screen.