The idea is that you build out your own little ecosystem and customerbase by heavily subsidizing the cost of your "product". Eventually, you either:
-Run out of money, and deploy your golden parachute.
-Monetize your customer base by offering paid services or increasing the price of your base services slowly over time while adding new "features" to justify the price increase to customers. Your large customer base means if done right you'll only make a minority mad and stop using your product and be able to rake it in.
-Another company buys you out in order to acquire your ecosystem.
Also found
This Security filing regarding MoviePass in particular.