ElVee

Salt-water is the deep end of fish tanks. You'll want to befriend a local pet or fish seller, particularly any that have amazing saltwater displays, because they know what they're doing. Maintenance is high, and initial buy-in can be expensive since you need to maintain a very specific water chemistry, decor, and fish population. Sadly, while they can look amazing, only other hobbyists will truly appreciate the effort of saltwater tank. Not that I want to discourage anyone, but it is the deep end. But if you have the money and interest, definitely start asking around local shops and do research on the Internet. There are tons of forums and sites dedicated to saltwater and they absolutely love sharing. And it is hard to beat the eventual beauty you can achieve in a saltwater tank.

If you want to go easier, a freshwater tank is far, far easier and cheaper. The initial buy-in can still be a bit spendy depending on what you want, and the learning curve will still spike for the first month, but once it gets going and things live for more than a month or two, it becomes minimal maintenance (food, some water cycling, some vacuuming of the substrate to get the excess poop out, changing filters, and getting rid of sick/dead fish). Definitely do research, since the start is critical, but otherwise it can be a great little hobby.

If you want to add live plants in your tank, prepare for more maintenance and a higher learning curve. But if you get past the first 6 months with a good-looking tank, you've made it and you'll have a beautiful tank with happy fish.