To be all about

What does it mean 'to be all about'?

"I'll show you what I'm all about."
"That's what the thing is all about."

I've read that and didn't understand what does that mean exactaly. Could anyone please answer me? Thanks in advance.

Actually I don't know if I can explain the first one. The second one is more just an emphasis of "is about"

1) I'll show you what I'm all about.".......this is an expression to emphasize a particular action that is about to follow.

For example:

If I were good at soccer and on a field with a group of friends, I might yell "I'll show you what I'm all about" and then do some sort of dazzling soccer move (I know this is a lame example, but this is difficult to explain).

2) "That's what this thing is all about."........This often denotes a deeper meaning to a certain event or action.

For example:

Let's say I was taking advantage of someone so I could make a profit without their knowing it. One person might confront me and say...You're just using him/her to make money. "That's what this is all about, isn't it?"