Hi There!
It's actually quite easy. My preferred method would be to go to wordpress.com and create a free account there (all you really need is an email address). Then once your account is created, you can start writing posts. As you write, your blog will take shape and be valuable to readers. Make sure to use a nice snazzy theme and design. Also, make sure to write on it frequently and you will automatically start attracting traffic because the blog will end up ranking for LSI keywords (don't worry, you don't need to know what that is). When the blog ages and as you turn 18 you can then monetize it and start pulling in money from Adsense, affiliate offers, etc. There's a lot of money in blogging so it's a good thing that it is your hobby ;-)
There are lot of sites through which you can create a free blog. Some of them are :
blogger.com
wordpress.com
Here is a video on how to create a free blog using blogger.com
Create google account and sign in to blogger.com That's how I got started.
blogspot.com
Hi, I am currently 15 years old (girl) and instead of making Youtube videos and such, I would like to become a blogger. How can I make my own website, safe, for free?