Twitch is a live streaming platform. It pays streamers on the number of subscribers he has. The platform costs $4.99 to each subscriber for a month of subscription to a specific channel. It then keeps 50% of t and gives over the 50% to the streamer. Hence, the larger your fan base the higher your earnings.
This is an efficient way of making a constant source of earning. You can conveniently start a streaming channel and post live streams of your games. If you manage to build your fan base you can end up with thousands of dollars every month.