Greetings: I am sure that there have been questions asked like this before, but kindly bear with me for a step by step approach to 'how it is done'

1). I come across a clip on how to do something from the web. Youtube, or some other site.
2). I wish to record it as it is playing. I am right there at the computer wanting to record this little clip and then save it.
3). I should be able to open up msrp, click on the region box and draw a square around the clip screen that is on my computer screen. (When I try to do this the clip gets hidden from sight).
4. What I would like for someone to do is take me please step by step though the stages from start to finish so I will be able to follow the sequence and save the clip.

Kindly assist anyone.

Thanks
Tiger155