I'm not convinced whether asking this question in here is right or not. But I think the phrase 'on the bottom floor' MAY BE a kind of idioms. I guess it means 'to succeed in' So, I write the question in here.
During the day, Brain attended shcool, and at night to support himself, he was a waiter at a downtown diner. On a good night, Brian brought home about $90 in tips. During a period of three years, Brian saved almost $1,200. One day at lunch, Brain's friend, Lance, told him about a startup company in Canada. "If you get in now," lance said, "you'll be in on the bottom floor. You'll make at least three times your money in only a couple of weeks."