it'd be a way in the door.
It would be a way in, through the front door: you can dream of being a high-flying executive, president of a company.....but to be able to work yourself up to higher levels of management in some organization by promotion, you first have to work for the company, to be able to walk through the front door as an employee. Having got a 'way in the door', you then 'climb the ladder of success'.
So, he's saying, 'it's a start. I'll be working for the company and then....'
Student or Learner