It's pretty easy to just set the trainer at a specific amount of resistance, and then ride it like you do outdoors. But to take advantage of power, and ERG mode, then as
unterhausen says, you need to have specific targets to achieve. e.g. 140% FTP, 200% FTP, etc - basically know your FTP and then target specific multiples above it. And then most training apps will have some sort of interval program based off your FTP. For me, I do HIIT stuff on The Sufferfest.