@Account Closed it looks like you have gotten a ton of good advice here. Your issue is not in learning the business, if you are truly dedicated that knowledge will come in time. I believe you see the real problem as getting the credit to make your first purchase.
There is no getting around the fact that most people and business will not loan to you if you don't have a good track record. This is the old chicken and the egg issue. Banks will not loan to people who NEED money. They basically loan to people who already have money and can pay back the loan at a later point.
Building up your credit by using a secured credit card, as @JT Spangler suggest is a great first step. Also as it has been suggested, increasing your earnings in a variable way is critical. Getting handyman or odd jobs that pay in cash help your pockets get fatter, but the banks will not take this into consideration unless you are getting "taxable" income. As suggested, pizza delivery is a great way to get more W2 income. Another way that I really espouse is to sign up with Uber AND Lyft and become an independent "taxi" service. You need to have a reasonable vehicle and a cell phone, but you get total freedom of when and how long you work. They handle all of the paperwork for you as an independent driver. All you have to do is answer your phone and drive people around. I have met many college students and nursing students who are putting themselves through school doing this. There is no reason an eager REI cannot do the same to fund a career. The other benefit of being a driver, either for a pizza place or as an independent taxi service is that you spend your time driving around neighborhoods. You are basically getting paid to recon your city for areas you might potentially purchase in.
After building up some credit and some cash reserves, I would recommend going to your parents for help. I am not saying you should ask them to dip into their retirement fund for you. But if they have good credit you might be able to have them co-sign on a loan for you. You handle all of the payments, insurance, paperwork etc and they just sign the loan docs with you. Of course this depends on your relationship with your parents, but I think you stated that you are living with them now, so I assume that they want to help you. Of course this puts them on the hook if you default...
Assuming you are able to buy a place, the next thing I would do is get as many roommates as possible and fill the house. Your only 20 so suck it up and share space for a few years and build up more credit and cash. I know it sucks to have to share a room and/or a bathroom, but the sacrifice made in your early years will payoff when you are older. Even if you get a duplex and rent one unit out, get roommates for the side you are going to live in. This adds income to your pocket that you can use to pay down the loan or invest toward your next purchase.
Back in my day, I did not have access to secured line credit cards or services like Uber/Lyft to work with. If they had, I would have jumped all over those options. However, asking the parents to co-sign and the roommates thing both worked well for me.
Good luck and make sure to let us know when you get your first place!
-Arlen