Striker Erwin, 21, signed a three-year deal at Elland Road last week despite having had just one season of first-team football in the Scottish Premiership with Motherwell.
"I'm here to progress as a player and hopefully develop my game then hopefully get into the first-team squad sooner rather than later," said Erwin, for whom Leeds will pay a compensation fee.
"I'm not setting any targets. It will take time. I've still got a lot to learn. I've only played one year of first-team football."
Erwin, who admitted it had been a difficult decision to leave Fir Park, was impressed by Leeds owner Massimo Cellino.
"He's great," the former Scotland Under-19 international said. "He's really passionate about his football and Leeds United, he's a great guy.
"I know Leeds have got a massive fanbase so I can't wait to start. It can't come quick enough."
Uwe Rosler, installed as Neil Redfearn's replacement on May 20, has so far made two summer signings with goalkeeper Charlie Horton also arriving last week from Cardiff.
Erwin added: "I spoke to the gaffer briefly and I'm really impressed with him. I'm really looking forward to seeing what he's going to do with the club next season and looking forward to starting pre-season with him."