Reading and writing is a cultural conversation. People write books to say something. Other people read those books and a few of those write books in return.
As has been pointed out many times, you should read. You want to write books and stories and contribute to the cultural conversation? That’s great! Read a variety of books in different genres, from different eras. Pay attention to what you’ve read, internalize it. This is exactly how native speakers learn the language.
You’ll find that books build off of each other. So read books that you enjoy. Read books from genres you loathe. (Well, skim them at least.) When things confuse you, ask a friend, what the hell is going on in this book? The answer may lead you to another book.
You’ll get, from all of this reading, a feel for tone, pacing, and story. You may even enjoy the reading! (It is important this not feel like a chore.)
All this reading will show you how words are put together, and probably help increase your vocabulary at the same time.
You do not need to be a grammarian to write. But you do need to learn to put a sentence together in a logical way. Most writers pick up grammar by osmosis, through reading.
Read through a good style book like The Elements of Style. It’s very short and is filled with (mostly) good examples of simple writing.
There are good books on writing out there. My favorite is Stephen King’s On Writing, but there are many others. The best ones are short and to the point and fun to read. (If the writer of the book can’t keep you turning pages, why would you take their advice?)
These books will teach you in a formal way what reading will show you: How to structure a story so the reader cares what happens next, how to make characters the reader would take a bullet for.
At some point, you’ll want to write. You won’t feel that you’re ready, but you should write anyway. Accept that you will suck for a while. That’s okay, all you have to do is write something better than the last thing you wrote.
Actually, you could start writing right now. Why? Because there’s an adage: We all have thousands of bad pages inside us, or dozens of pad paintings, or terrible songs. The goal is to get them out of us by creating until our ability catches up with what we want to be able to produce.
Get feedback from people whose work you respect: Reading groups, editors, beta readers, and agents. (“Feedback” from friends and family is usually just friends and family discharging an obligation.) Revise.
Important: Finish what you start.
Believe in yourself. Keep writing, no matter what.