Still do not understand steemit? Help me!

Dear Steemit Friends,
let me be honest and confess. I do not understand the intricate complicacy's of Steemit. YES, I have started in August 2017. Its already too long but its never late to ask.

I focus on building a strong content. But that's its.

Today when I was browsing through my account I saw that my estimated account value is 64 dollars. Is this good? Does this means that I can now, if I want withdraw 64 dollars?

What is steem Dollars? steem power?

How do people do trading here?
Is anyone willing to explain me in Details please?

Thanks in Advance !