hold常用来表示用手拿住或者抓住，hold your end up的意思是：做你份内的工作，也可以说，承担你份内的责任。

【例句】
Joe isn't a bad guy but he simply doesn't hold his end up, so I have to work late every day to finish what he doesn't do.
Joe这个人并不坏，可是他就是不完成他份内的工作。我每天得加班做他没有做完的事。

You're not holding your end up. We're having to do your share of the work。 　　
你没有做你该做的工作，我们替你做了你的那份。