I dont have access to a bike so recently all I have been doing is steady riding on the stationary. How much gains am I actually making from using an indoor stationary bike? Are there any workouts I can be doing on them to get me more fit?
You can get monstrously fit on a stationary bike. As with any workout, you have to induce overload. That means riding longer, harder, or more often. Choose any two for each 2-3 week training period and then change it up for the next block.
The only problem most people run into on a stationary bike is that they fall into a rut of just turning over the pedals. You have to work hard and be willing to sweat buckets. The Spinervals videos are a good place to start for some workout ideas.