I don't see how buying junk means a job...?
A company sells a product called "ItemA".
You come along and buy "ItemA".
The company makes money from selling "ItemA".
The company wants more money so it orders more "ItemA".
The company sells more "ItemA" and earns more money.
Now that the company has more money it can hire more people at a higher wage.
Because of it's extra costs in hiring people it gets more "ItemA" and sells more "ItemA".
As the company gains more money from selling "ItemA" it in turn gives more money to other companies.
The company that produces "ItemA" will earn more. Marketing companies for "ItemA" will earn more. Packaging and Distribution companies for "ItemA" will earn more.
These companies earn more money and they too can hire more people at higher wages.
Now that there are companies earning money from "ItemA", you can get a job in a company and earn more money for yourself and your family.
As a basic principle, buying more means that shops can sell more and hire more. It requires more than just one person buying, but it does technically stimulate the market at a tiny level.
It's why recessions are difficult, because people stop spending as much because they fear they will lose money.
The less they spend, the less shops earn and the less money gets put back into the economy.