Gardens Inc.: From Rakes to Riches

How do I go about "collecting" money in this game? Sometimes it asks that you collect money in a particular chapter. I have no idea what they are talking about. Then, later on in the game, it has the money listed up at the top (actually, it is a picture) but I have no idea what earns the money and what makes it fluctuate. So far those are my questions. I hope some one can help.

Thank you so much for the details. That helps me a lot. Also, thanks for answering so quickly.