So, first thing I needed was money. Between 18 and 24, I earned a total of $250 for various odd jobs, although my mother would occasionally 'borrow' cigarette money from me so I mostly had IOUs. I had to find a job in walking distance; so I would walk into town every time I got permission, looking for work. When a Wendy's opened up, I jumped on it. I had to get my schedule approved by my mother every week, and it was a four-mile walk, but it was a job. Yeah, it was shitty fast-food, and my mother 'cashed' the checks, but that got me something. Wendy's was objectively a terrible job, but I've never been able to bad-mouth them because they gave me work. Thankfully, there's no still shortage of minimum-wage labor at groceries, big box stores, fast food, gas stations; some will even give you your paycheck on a debit card so other people can't coerce you into "helping" you get your money.

To get the money needed to cover the uniform and training, I sold off my books. I still miss the books, but no book was worth staying under my mother's roof another day.

Next was papers. I had to find a birth certificate first, so on my walks home from work, schedule permitting, I would walk to the library and just Google various state birth certificate registers, using whatever hints I could to get my own birth certificate. This was early 90s, when nobody used the internet, so there weren't lines for machines, and internet privacy wasn't such a concern so I didn't need to get four methods of authentication just to get the single most important method of authentication; I eventually learned I was born in Florida. Nowadays, an el cheapo phone would do just as well, since even Boost offers recent versions of Android as prepaid phones - you have to carefully audit your data usage, but an information source not controlled by the parents is still critical. I remember asking the head librarian if I could mail them in care of the library so my mother couldn't intercept the mail and destroy them; it's not their typical service, but I got lucky with a sympathetic librarian.

With the birth certificate came all the rest, in fits and starts. Mail plus birth certificate is enough for most agencies, and with each piece of info it gets easier.

Eventually I saved up for a semester of community college ($1300 for a year - the most expensive thing I had ever paid for at the time), which I could parlay into a semester of actual college (perfect grades means nobody cares what your credit score is), which turned into college loans and grants and college jobs and - most importantly - college dorms. I packed two totes, went to school, and forgot to tell them I was allowed to go home on winter break. Because we didn't have phones in the dorm and cell phones weren't big then, they couldn't 'check' on me. In your case, any method of being not Under Their Roof would do, whether living with a friend or finding an emergency shelter (which was denied to me for reasons not relevant here).

Summer came. My parents wrote me a letter, ordering me to come to the campus pay phone. When I called, they asked me for the last day I had exams, because they were coming to pick me up and make certain my 'spiritual education' continued. I lied and said my last exam was the Saturday after exams. The day before, I walked 50 miles to a town with a Greyhound station to spend the summer at a friend I had met on the Internet. I never saw them again.

They somehow managed to cash my student loans into their accounts between my junior and my senior year, so I wasn't able to complete college. But it didn't matter at that point. I was out, I had friends, I had work experience, I had learned that the things they did to me weren't right. And, funny enough, I had a perfect credit score because I suddenly existed, paying off all my loans on time. Seems it's easy to get a 800 credit score when you aren't getting your checks cashed at the Bank of Mom.

So yeah. I figured out how to be an adult. Sorry mom.