MT is an abbreviation for Morse Taper, which is a very common type of taper for drill presses. The maker will choose an appropriate numbered MT fo the size of drill press. MT1 is quite small. MT2 or MT3 would be common on many drill presses or lathe tailstocks. MT4 would be largeish, and there are several higher numbers for "really big" machines.
JT is an abbreviation for Jacobs Taper, which is a fairly common type of taper for drill chucks. The Jacobs Chuck company has many different numbered JT to fit different models, and they are not all ordered nicely from small to large.
Usually, you get an arbor which is, for example, MT3 on one end and JT4 on the other end. The MT3 end goes into the end of your drill press spindle, and the JT4 end goes into the end of your chuck. When you extend your drill press quill all the way (assuming it has an MT taper), you will see a slot and the tang on the end of the arbor MT taper is visible in the slot. You need a wedge that goes in the slot in the empty space at the end of the tang. When you strike this wedge, it will pop the arbor out of the quill. At the other end, the JT taper is not frequently disassembled. Usually you get a pair of slotted wedges that work between the back of the chuck and a shoulder on the arbor. Squeezing the two wedges toward each other will pop the arbor off the chuck.
You can also buy drills with MT shanks, and IMO these are a better choice for large drills than using an oversized drill chuck. If you have a drill with an MT1 shank, but your drill press has an MT2 or MT3 spindle, you can buy ground adapters with an MT1 internal taper and an MT2/3 external taper.
TL;DR; Don't buy a drill press with a JT on the end of the spindle. Buy one with a MT inside the end of the spindle, and get an MT/JT arbor to hold your drill chucks. This may be the way your prospective drill press comes (!) but the advertising copy may be confusing.