From Day 2 onward, you can automate your Business!
Automated businesses don't require you to manually collect cash while the game is open and they will keep producing Cash even while you're away from the game.

Each Business has its own automation requirements, which varies according to the Day you're on.
You will first need one specific Manager to be unlocked and at a certain level. If you meet that condition, all you have to do is pay the required Cash.