To answer each point in turn:
- DMR radios are different from "normal" ham radio equipment in that it uses a digital voice encoder/decoder rather than the more traditional FM analog voice mode that you're probably used to. Fun fact: Kenwood makes DMR-capable radios in their NX series of digital (commercial land mobile) radios, and the mode was made popular in commercial circles by Motorola. So the voice mode has been around for a while, just more recently coming to amateurs via the explosion of Chinese-made models
- As mentioned, this voice mode was originally found in commercial rigs. Two of the most appealing benefits of DMR (and generally, YSF/C4FM falls into this as well, D-STAR a bit less so) is that the voice quality is extraordinary, no background hiss that you get from analog FM; additionally, the range of DMR radios (for the same amount of power output) is far superior to analog FM radio. In fact, you'll generally get very listenable content up until you're right at the absolute range limit for the power level of the radio. There are more benefits (and a few drawbacks even) but this is a high-level overview, right?
- DMR radios these days very often come in dual-band VHF/UHF models. However, most of the big names (Kenwood and Moto) are UHF or VHF, not both. Since Motorola was early on the scene with DMR, a fair number of repeaters use Motorola hardware, and use UHF frequencies. More recently, there are voice modems that you can patch into analog repeaters to bring digital voice modes like DMR to existing analog hardware. It's a pretty wild scene out there.
Since you asked about simplex in your comments, DMR can absolutely be used for simplex comms (this would be what people would call "Tier 1" DMR) and the general consensus for amateurs is as Glenn W9IQ put it here: program your DMR radio to color code 1, time slot 1, and talk group 99.
All the vocabulary (color codes, time slots, talk groups, and the oft-misunderstood CPS software) are all challenges that await your interest or pleasure, depending on what you're into with this hobby.
Have a great day!