Welcome Alex!
Boy I wish I would have found this site soon after I graduated high school like you did! How lucky you are at such a young age!
I know how you feel in your head right now.....so many questions....so much to learn....overwhelming for sure!
I think you should read over the entire introduction before you try to get all the info in chapter one learned and digested. With time it will come. Keep reading, keep listening to the pod casts, etc. and it will all start to make sense.
With that being said, I can help a little with your "buy and hold with property management" question. I have some experience under my belt with one single family home that I rent out in the Phoenix area. The state of Arizona requires one like myself to hire a property management company to manage my rental because I don't live in Arizona. I live out of state in Utah. I prefer to have a property management company anyway because of that very issue. Property management companies vary in how they do business, however, it generally works like this: You pay a fee up front for them to advertise your property for rent.....they screen tenants for you....and once a tenant is chosen and move in, the company then charges the owner (like me) and the tenant a monthly fee. I get charged 8% of the monthly rent collected. The tenant also pays a small fee on top of their rent. There are other fees too, like maintenance fees, trip charges, administration fees....all for them to manage all the day to day dealings with your rental.
The buy and hold part just means that you buy the property and hold for the long term before you sell it or some other exit strategy. Over time, you will hold this property and eventually pay this property off and hope to keep taking in all the rent money, minus fees and expenses, a.k.a. cash flow, and you have what is called "passive income." And/or you buy and hold for appreciation and rake in all that equity when you sell.
Hope that helps! Slow down a little and learn one thing at a time, then move on to the next topic. You will just confuse yourself, get overwhelmed and give up if you try to move too fast! ;)