Literally means 'I'll assume responsibility and control of this situation from this point forward.'
It's usually used in a condescending manner, with sarcasm optional. So, in reality, it means, 'You've screwed up enough/underperformed the task, so I'll assume control and responsibility so it won't become FUBAR
New guy at job - "Hey, I transfered the account to Mrs. Jennings like you told me to!"
Boss - "WHAT?! I told you to transfer the funds to Mr. Jennings?! I'll take it from here."