Turn your bicycle into an exercise bike. Simple to use and easy to store when spring comes around. A standard indoor trainer has a stand to support your bike at the rear wheel and a resistance unit driven by the rear tire. Some models have adjustable resistance. You will need a smooth tire (There are trainer-specific ones) an all metal quick-release, and a front wheel block to level out your bike.
Smart trainers take an indoor trainer to the next level. The trainers' resistance unit has built-in electronics that, at the very least, transmit your speed to capable devices. (Bluetooth or ANT+)
Fully smart trainers have the ability to be controlled remotely by software on a computer, phone or tablet. The app controls the resistance so you don't have to mess about with it. The trainer also measures your power output so you can train to a precise target.