I can't get into the video but what are you having a problem with?
Bro = short for "brother", a common endearment between friends in some cultures
Maybe = perhaps
You ought to = a suggestion that something is a good idea
Rest = have a break, relax, stop using for a while
Your arm = self-explanatory
Without the video, I don't know what the two people are doing but the first speaker ends up suggesting that his friend should stop doing whatever it is he is doing with his arm, at least for a while.
If you think that the subtitles don't match the words, you might be right. That happens quite regularly.If the subtitles don't fit what is happening on screen at all, then it's an error.