Do you have a local hobby shop where you can look at sets? That would be very helpful. If not, and your budget is $200 or less, there is really only one choice and that's a Lionel LionChief starter set of some sort. Probably from Amazon or a good internet retailer (look at Charles Ro, Nassau Hobbies, or another forum sponsor)It will come with a small steam loco, likely a few freight cars and Fastrack, which can make a small loop of track about 40 x 60.
The advantage of LionChief is that if you decide to expand and buy some more track (say another loop from a second LionChief set, plus a few extra straight track, or even a pair of switches), the second locomotive can be independently operated with a second remote. Just don't buy two of the same set (each set loco is uniquely linked to a specific remote).
Thus for an investment over the next few years of perhaps $400 to $500 you wind up with command control for two locos, and two loops of track if you buy a few extra straight tracks. Compare that with the the higher quality but more expensive MTH sets, at about $300 each, and in order to have independent control of your two MTH trains, you'll need MTH's DCS, which is another $300 or so. So $500 versus $900 for somewhat equivalent functionality.
In any case, unless you can come up with an extra $100 or so, you're "stuck" with Lionel starter sets. However, that may be a more suitable solution as you will achieve independent future functionality in the loco (LionChief) right off the bat, superior track, and significantly less initial expense. The Lionel loco and rolling stock will be adequate quality and detail, but almost certainly significantly less so than the more expensive and more detailed, robust MTH rolling stock and loco.
The alternative, which I don't recommend for a beginner without expert experienced advice, is reasonably inexpensive conventional used equipment (I'd go with Lionel postwar or MPC for price), which will be in rougher shape than new, but good value. The problem here is it will have to be bought from used equipment sellers without a warranty, unless you have a dealer who sells used equipment with a dealer warranty. Without experienced help, I'd go with new stuff. If you buy something from Amazon or Charles Ro and it is defective, they will exchange it or refund your money. That's reassuring.