You have to start by coding your own engine. Start from the scratch argument (from http://www.connorlinning.com/game-development-and-archaic-elitism/):
“I want to learn to play guitar and play in a band. Where do I start?”
“Well, first off, you’re going to need to learn how to make your own guitar from scratch.”
“Not only that, but you’re going to need to create your own recording software similar to Pro Tools. Don’t use Pro Tools. That’s for sellouts.”
“Are you sure? I just want to play music and write some albums.”
“Come on, a real musician will make his own instrument and recording equipment. Don’t take the easy way out and only learn to play the guitar. Trust me. You’ll be such a better guitar player after doing all of this.”
Stupid right? Just pick whatever (eg. game engine, programming language, even google forms) and create!