Welcome. Was in the same position as you last year, and there's too much content to go through in one post, but my advice would be to find a local bike store and talk to a salesman. If that's the area you're going to ride in, then they will know what sort of trails you'd be riding most often, as well as the type of bike you'd need for them. However, do as much research as possible before making a purchase, so you know what you're in for before being taken for a ride. Bikes come in all shapes and sizes nowadays, and one bike might be suitable for one trail, but not the next.
I managed to buy something 2nd hand for a good price, rode it for a year, learnt the ins and outs of the bike in question, and what it's capabilities were, and then when I knew exactly what I wanted (needed), took the plunge and bought new. The new bike now ticks all the boxes, and is a massive upgrade to what I was riding. It took me a year to figure out though how much travel in the suspension I needed, what sort of tyres work where, and whether I would be more interested in trail or enduro riding as opposed to cross country. There are tons of bikes in the 2nd hand market at the moment, so i'd probably start here once you have an idea of what sort of riding you want to do.
Good luck mate. So much to learn, but be prepared for a shedload of fun once you do
