knew / found out / I've known

Lately I'm learning English expressions through several new methods.
Today, I watched Michael's 5분 과외 video about common mistakes.
This video taught me the difference between '알았다' and 'knew'.
I didn't know what 'find out about' means exactly.

If you find any mistake in my practice writing, PLEASE tell me about it.
Thank you!





knew (used to know) : 알았었다

e.g. Back then, I knew how to speak Chinese, so I had no trouble getting around.

• practice
• She and I knew each other back in elementary school.
• I knew her name back then, but now I can't remember anything about her.

found out : 알게 됐다

e.g. I found out about your site since last year.

• practice
• I found out about Google+ community a few months ago.
• I found out she doesn't love him any more.

I've known : 알아왔다

e.g. I've known about you since last year.

• practice
• I've known my best friend for almost 20 years.
• I've known the truth from the beginning.