Rich Dad Poor Dad outlines the concept that the rich acquire assets that generate income, while the poor and middle class acquire liabilities that cost money. It discusses that assets are things that put money in your pocket, while liabilities take money out of your pocket. The document contrasts the cash flow patterns of wealthy people who own assets like real estate, stocks, and businesses, with poor and middle class people whose cash flows from jobs and are spent on expenses and liabilities like mortgages.