Online virtual cycling platforms such as Zwift, Sufferfest and Peloton are good options as they provide both structure and an element of social interaction, be it on the screen. They do require you to buy or borrow some equipment to make the most of it. GCN did a good Video recently on the basic needs for indoor cycling.
If you are not into virtual training, an easier option is to use a spinning bike, or your normal bike on any basic turbo trainer and then create your own playlist on your favourite music device or search for a suitable cardio/spinning playlist on Spotify or Apple Music. Just pay attention to the beat and spin away.
GCN’s YouTube channel has a lot of cool videos to keep you entertained, but also a great library of free Training Videos to also keep you motivated, even if you’re not hooked up to any of the virtual platforms.