It depends on the context. If you are working on the computer and s colleague reminds you to 'save it', it may simply mean to save the documents in case of a network problem. But if you have made a big mistake and you start to try to make excuses or apologise and the other person says 'Save it!', they are being a bit angry or hostile and saying they do not accept the apology. In effect they are saying 'keep your excuses, because i dont want them'

Thank you.

Be quiet - yes, it can be that. Or it can mean something more like: 'don't say it now, say it later'. As Karen said, it can refer to documents on a computer. It can refer to reserving things like food. It can refer to preventing a goal, e.g. in football.

I heard that, it can be a way to say "be quite" in a rude way but some of those videos look different. That's why I got confused.

It can mean several things. That's why I asked for context. Showing us a collection of what I assume is hundreds of videos that have that phrase in it does not really help.