We use this expression to tell someone to stop talking about something.
You can use this phrase in ………… language.
A: Petr’s boss gave him a laptop, a new company car and ten thousand shares.
B: Give it a rest about Petr, will you! I don’t want to hear about him any more.
A: It’s got a great engine, and it’s only done 15,000 miles. And –
B: Give it a rest! I’m not interested in your car. Let’s talk about something different.