Firstly, congratulations on nearly reaching the starting line to the rest of your life. 18 always feels different to different people, but mostly everyone finds that life changes quite rapidly after that level-up.

People here have mentioned getting a job, but I want to offer a bit more actionable advice:

1. Contact a temp agency. You might find a direct employment somewhere if you scour the landscape enough, but temp agencies almost always have a contract in need of someone who is willing to show up. A lot of industries use temp agencies to fill in gaps but also to headhunt, and temp-to-hire is a real possibility that could translate into a career. Do not let anyone try to dissuade you from using a temp agency. Especially for those lacking work experience, they are likely your best bet(that was how I began before I was even out of Highschool a decade ago).
2. The fact you are actually working on a website(HTML from scratch or at least some custom HTML usage I would hope?) is really cool! But let it be a side-hobby until you can get enough of that experience under your belt. If you get well-versed enough in web design, you could always freelance for experience and possibly translate that into an opportunity down the line.
3. Starting a business is a lot a lot of work. It is not something a greenhorn(those new to things) should really be vying for, though the ambition is to be admired, I did not have that kind of thinking when I was your age. More power to you there, but do not get lost in the sauce. Like I mentioned in point 2, perhaps you can translate your apparent passion of web design into something eventually, but first you need capital and stability.

I am not going to offer financial advice since, well, I cannot do that. But the above is general job advice from a girlie on the boulevard, you can take it or leave it. I will opine one thing though: Banks usually have a way to automatically transfer money to a savings account and you can set percentages when setting up direct deposits so you can put money in one per paycheck, if you feel so inclined to do so. That is up to you and your situation though, just mentioning it if you were unaware of that.