They have their own business and know that if they expand, they will make more money. First they need to have capitol. They are away at school and their car breaks down in some small town. They need to buy books at school and their student loan has not come in yet. Credit increases private sector demand.
Businesses increase production to meet new demand.
New businesses form to compete for expanded markets. Businesses hire workers for new plants, which creates new demand. Return to number 1.