I'm 15 and i'm writing a book -?

Well, unless you are writing to 15 year olds in the voice of a 15 year old, write like an adult to adults. No wanna, kinda, i, and like seriously almost. It brands you as a kid who just slapped down whatever came into her mind and who did not edit her work.

I think it is great that you are almost finished and that you did spend time creating more than one draft. It shows your commitment.

Below is the url for my search "self publishing" in my library catalogue.

See if your library has those books or other books in that subject area and Dewey Decimal Class number.  If your library has restrictions due to Covid-19, check their website for help or call your branch to see if you can put them on hold and pick them up at their door. I'm more comfortable with information in books than on the internet, though the internet may have good, up to date information.

Oh, and be sure you and your parents read and thoroughly understand any contracts before signing them.  Like Amber said, it's a business, not a game, and there are sharks who rip off the unwary.

If you self publish, you will spend $1000 and your book will be advertised on Amazon.  A colleague of mine tried this, he wrote a detective novel.  Apart from myself and a few of his relatives he has had no takers.  If you do this, do it for your own satisfaction. Otherwise resign yourself to writing about 27 drafts under the instructon of a publishing house.

If your work is any good, a real publisher will be interested. If it's not, you can put it online if you like, to get some critiques, but you'd be better off just continuing to work on your writing and eventually taking some classes in order to get some professional guidance.

Never consider it finished till you have had several readers go over it.  Listen to their comments on plot structure,  dialogue issues,  plot holes and anything else that bothers them.  Fix the issues and give it to another round of readers who are also to look for problems as well as check your spelling and context. 

My advice would be to spend some time learning about the industry. If you self publish how do you intend to pay for it? You don't work yet, I'm assuming and it is very expensive.

Secondly, you've almost finished it (congrats by the way) but now the real work begins. You have to edit it. Which is more than just correcting spelling and grammar. In many instances it's a total line edit. That can take months, even longer if you don't know how because you'll need to learn. Then you begin giving it to beta readers for help to improve it, and believe me, there will be tons of improvements suggested. Because you are so young and your grammar and spelling in this question was poor (you may not write a manuscript like that) you may need a professional editor.

Self-publish material is constantly getting flack for poorly turned out material and poor writing skills that haven't been effectively cleaned up by someone who knows what they are doing - don't be one of those people. To get your manuscript to publishing standard should take a few years. You're only 15 and this could be your first completed manuscript. This isn't a game, it's a business and you need to know what you're doing to avoid the sharks and murky waters otherwise your book will be a flop and you'll have achieved thing or you'll get ripped off.

You'll be able to tell people you're published, or more that you published yourself, but that means nothing when you have 0 or terrible reviews. Or your reviews are just a sea of people who have read your work only because you gave them a free copy for an honest review - don't be one of those people. It sends a red flag you don't know what you're doing. Learn your craft and learn your business.

i would talk to a publisher about it

If you're self publishing it, you're free to do as you like. My advice as an English professor with a background in editing and publishing I suggest you try shopping it a little to see if publishers might be interested. Speaking frankly, you (and most new authors) have little chance of getting signed, but 1) you never know and 2) some helpful criticism and advice can be really beneficial. You're a young writer and clearly compelled to write if you've already written a book, so you have the basic ingredients needed to be a writer - writers write!, but you may lack knowledge and skills to both navigate the waters of editing and publishing and working with editors and publishers. Good luck! 

i would contact a publisher about it