It means to not do something for that time and do something else instead. If someone says to you 'take the weekend off' from doing something, they're implying you're doing to much of it and that you should have time to yourself, or just have fun.
Some examples being~
- How about instead of studying, take the weekend off and come watch a movie with the rest of us.
- I've done so much housework over the week, I'm taking the weekend off and doing whatever I want.
- The boss is letting me take the weekend off as I'd done extra during the week.