These inflatables are towed behind a boat with a tow rope or harness. They come in a variety of shapes, styles, and colors to fit everyone's personality. Most of them are brightly colored (in whatever shade) so that they stand out on the water. There are ones meant for one rider at a time, and there are ones meant for multiple riders of two, three, four--all the way up to a dozen. Some people prefer riding alone, but if you're looking for boat towable toys for the whole family you'll probably want to look into ones for multiple riders.
This is a water sport, but not one that requires much skill. You just need to be able to hold on tight, and be a strong swimmer in case you fall into the water. The ride itself is a lot like riding on a roller coaster. It start off slow as the boat takes off and then the inflatable gets some air and starts gliding above the water, picking up speed and giving the riders a great thrill. Where a roller coaster would end in a few moments, however, you can keep riding on an inflatable as long as you want.
For safety's sake make sure you have life vests, that everyone can swim well, that you have a tow rope in good condition, and that you follow any posted safety regulations where you're going to be at for the day.
Picking boat towable toys for the whole family can be a confusing job when you're unfamiliar with your options. Narrow things down by the number of riders you're looking for it to hold and what styles you prefer and you'll save yourself a lot of time looking over your options.