There are two main categories of trainers:
- Traditional, "wheels on" trainers, where your bike is held by the rear wheel, which runs against a roller that applies resistance. All inexpensive and mid-priced trainers are this type.
- Newer "wheel off" trainers for which your remove your rear wheel and mount the frame directly to the trainer. Price-wise, these are the upper midrange and high-end trainers.
- There's actually a third category that has burst onto the market recently and that's dedicated trainer bikes. These are standalone bike simulators that are really interesting, and really expensive.
In terms of interactivity, less expensive trainers will be "dumb", meaning that they have no connectivity options. You adjust the resistance by changing gears (and perhaps with adjustments on the trainer) and choose your preferred form of entertainment to keep you motivated.
At the higher end of the spectrum, you'll find "smart" models that offer computer connectivity that allows apps to control the trainer's resistance and simulate real-world road conditions. This includes actual videos of rides through services like Rouvy, or simulated rides and races through services like Zwift. The smart trainer experience is much more immersive, to the point that you'll find yourself trying to steer and lean the bike into corners. It's really a huge leap from older trainers and actually makes indoor riding - dare I say it - fun! The two leaders in smart trainers are Wahoo and Tacx, but Saris (formerly CycleOps) and others make similar products. If you want to geek out on reviews, I recommend going to
https://www.dcrainmaker.com/, as there's a wealth of good info there. FWIW, my girlfriend and I both have the Tacx Neo and they're great, but they should be for what they cost. Some of my cycling buddies have the Wahoo Kickr and they swear by them.