What's the main difference between a "thief", "robber" and "burglar"? Are they all interchangeable?

Is "come one, come all" an idiom? What's it mean?

That's right. "Come one, come all" is an idiom! It means that everyone is invited. Kind of like, "come every individual, and come everybody!" Ex: We're performing a show this afternoon. Come one, come all! Ex: Come one, come all! To our restaurant opening this weekend.

What is the meaning of the idiom “hang in there”?

“Hang in there” is a phrase used to encourage someone to not give up during a tough situation. For example, if someone was telling a friend how much they were struggling studying for a test, their friend may say “hang in there” to encourage them to keep going.

What's "get turned around" mean?

To "get turned around" means to lose one's way or become lost. Ex: I'm sorry I'm late! I got turned around on the way here. I had to ask for directions. Ex: She got turned around and couldn't come to the party.

What does "jot something down" mean and when can I use this expression?

"Jot" here means "write," so to "jot something down" means to "write/note something down." You can use this expression when you want to express that you will write something down to remember it. Ex: I jotted down some notes during my work meeting. Ex: Can I borrow a pen? I need to jot something down.

What does "old maid" mean?

'Old maid' is a rude term indicating a woman who is considered too old to marry by society. Ex: She is an old maid.