1-  learn/know the ropes

Meaning: learn/know how to do something 

This comes from a sailing or nautical type of reference because ropes are something we use when people are sailing.  

When people sail on yachts and boats they have to tie up the boat in a certain way. They have to pull certain ropes to get the sails to move. So to learn the ropes is when you’re trying to learn how to sail.

Example:

He’ll be fine. Just give him a few weeks to learn the ropes, and then he’ll be as good as anybody else.

2-  carry the can

Meaning: take the blame or responsibility for something that goes wrong

Example:

Somebody is going to have to carry the can for this mistake. So who’s going to take responsibility?

3-  burn the candle at both ends

Meaning: do too many things in a short period of time; work hard and play hard

Examples:

Well, what do you expect? You’re burning the candle at both ends. Something will happen. Either your work will start to deteriorate and that will be a problem, or you’ll get totally exhausted.

4- hanging by a thread

Meaning: you’re in a dangerous situation; for example, you’ve had a warning from your boss

Example:

Your future is hanging by a thread. If you don’t improve your work, I’m going to have to fire you.

5- off the hook

Meaning: no longer in trouble

Example:

Good news, you’re off the hook for this weekend. I’ve got somebody else to do it.