On Tuesday, 36-year-old Queens native Leo Grand launched his mobile app, "Trees for Cars."

The app is designed to get people to carpool and reduce the amount of carbon dioxide in the air.

Grand is homeless, and just three months ago he had no idea how to code.

Patrick McConlogue, a 23-year-old programmer, would pass Leo on the street on his way to work each day. So one day, Patrick offered Leo $100 or the opportunity to learn how to code.

Every day for the past three months, the duo met to study and create the app.

McConlogue and Grand's journey, followed by 50,000 people on Facebook, is only just beginning.

"He writes every line, and he understands every line," McConlogue said of Grand.

"If you've been blessed with a talent or skill…pay it forward, teach somebody something. Even if you just one help one person, the fact that you even tried is a step in the right direction," Grand said.