How to become a Author ?

You don't approach anyone with an "idea" for a book.  Anybody can have an idea, or concept for a book, but that doesn't mean they can write one. Write your book, then shop it around to some agents to see if somebody wants to help you get it published. Or, publish it yourself using a self-publishing company.

The only time I can think of where you would approach a publishing house with an idea for a book would be for non-fiction work and you'd either have to be famous or have something interesting/useful to offer that would 99% guarantee adequate sales.

For fiction, there's really no such thing as selling an idea for an unknown author. You'll have to write the book and then either self-publish or find an appropriate agent to submit to or submit to a publishing house that accepts direct submissions.Step one for fiction would be learning how to write a novel, though.

Publishers and agents don't give a rat's butt about ideas. They want completed manuscripts that are well-written and free of errors.

First step to becoming an author is to write. It's that simple and also that difficult. You will have to learn your craft and be willing to accept criticism. In the beginning just about everything you write will suck. This is totally ok. Be willing to make mistakes. Big, nasty ones that make you cringe as you improve.

Above all else, know there is no fast and easy to way becoming an author, especially a published one. You can, in theory, crank out some poorly written drivel that you put up on Amazon Kindle for $0.99, but it won't sell more than five copies if you're lucky. Be smart, do your due diligence, and don't be in a rush to call yourself a published writer. Good luck.

maybe you can take some writing classes

What's the distinction between an essayist and writer, you inquire? Incredible inquiry.

While essayist and writer are utilized reciprocally, there is certainly a distinction between the two. A writer is an essayist, yet an author isn't continually going to be a writer.

1. Write your book first.  
2. Rewrite it 4 to 8 times to get it publication ready.  
3. Have beta readers read it and listen to their comments. 
4. Do another rewrite. 
THEN you can consider publishing. 

You should write the book first.