Write it. Even if it's just for you.
I think this is an incredibly important and valuable question, because I hear it all the time from many of my friends. They aren't writers or authors, and they have limited professional training or experience in writing, but they have a book in them that is screaming to get out, and they need to put it on paper and bring it out into the world. They have a story that needs to be told, whether it be a fictional story, a fantasy world they've been building, or just a story from their life.
But I think the question you might have is, how do you do it? Will anybody read it? How can you just... make a book with no training or experience whatsoever? And even if you do decide to write a draft, it's going to be terrible and no one will want to read it, right? When it comes to this book that's crying out to get out of you, I think you might be asking yourself, would anybody even care?
I'd like to digress for a moment to tell you a story.
My grandfather passed away when I was in high school. Before he passed, he always talked about his life and his experiences - fighting for his country, being in the Boy Scouts, growing up in a tough part of the world and learning important lessons. I loved his stories because he was a man who had seen so much, and lived a rich and beautiful life. After he was gone, I suddenly realized that all of his stories, all of his life experiences, even if we all remembered them secondhand... all of his firsthand accounts had died with him. There was nobody left to tell his stories, except for us.
He wasn't a writer, but he had always talked about wanting to write a book about his life, all of his stories, so that we could read about them someday. He never got the chance to do that in life, and we always regretted that he didn't.
If there's a story that is crying out to get out of you, write it. Just make a draft. It's okay if it's bad, or if nobody else ever sees it. It's okay if you feel like you are not a good writer, and that people will hate it. You are putting something out into the world that you love and treasure and that people will value not for its quality, but because it came from you. My partner is not the best poet in the world, he freely admits it, but I don't care. I love reading his poems anyway because they come from him. You don't even have to publish it. Write it for you. It doesn't have to be for anyone else.
And if you learn a lot from writing it, then you can always come back and write it again! You're not forbidden from writing the same story twice! If you're worried about wasting your best idea on a terrible first draft, don't be. You will learn so much from writing that terrible draft one that you'll want to write draft two and make it even better. The love for the story won't die just because you wrote an awful version of it.
Obviously, since you are a first-time writer, you are going to have a lot to learn. You should absolutely attend seminars, take classes, learn the art of writing, and study as much as you can. Read, read, read, and learn from what good authors do well. To fully tell your story in the way you want to tell it, you'll have to learn how to write well and communicate effectively in narrative form, and that's a lot harder to master than it seems.
Other resources that may be helpful: