Butted refers to the way the tubes on the frame are joined together, some joins are stronger than others. GT frames are very distinctive in the way the tubes join under the seat (see the little triangle there?) and they are perfectly good frames. It should be quite light and sturdy enough for what you're going to do.
The front and rear mech are the things that move the chain from one gear to another and the shifters are the triggers on the bars that operate them. The GT has Shimano ones. Very low-rent Shimano is labelled 'SIS' or nothing at all. Then the ranges are named, Acera, Alivio, Deore, etc. Acera is quite low-spec, it will work fine but the trade off is mostly durability. When they wear out replace them with better quality items like Deore which will last longer.
24 is a good number of gears to have. Put simply, to fit more gears in the cassette (block of gears at the back) and chain have to get thinner, which means they wear out quicker. The most durable set-up is 21 gears but the extra gears of a 24-speed set-up is, in my opinion, worth having. The next step up is 27 and I don't think the extra gears there are of much worth, I have 27 and often shift two at a time. To prolong the life of your gears buy a chain checker and fit a new KMC chain when it reads 1% worn.
Quick release wheels means that you do not need spanners to take the wheels off. Lever-operated cams unfasten the wheels in seconds for easy puncture repair or packing into the car. Read the instructions to use them safely.
You know what hydraulic brakes are? Same as on a car. Little maintinenvce should be required if set up correctly but again, observe precautions to avoid trouble.
Oversized bars means that the middle section of the handlebars is thicker than the ends for extra strength.
Most of the other stuff is just the names of who's made the part, like Tektro, Alex, Suntour etc. No big deal. It's mostly par for the course at this price point. Over all it's a perfectly good spec for the money and a decent frame that will stand upgrading as parts wear out.