The suggestion to read the "pinned" topics in the New Shoppers area is a very good one and will give you some real insight into this business.
You will find that Mystery Shopping is about the single most flexible gig you can find. We all use it a bit differently to fit our needs. Most folks do it as a side gig to supplement incomes. There are a handful that shop full time. There is money to be made here - and personal expenses (such as oil changes) you can eliminate from your budget. They key is to educate yourself and put some time into getting yourself going. The good news it that this forum is completely free and folks here will share a tremendous amount of wisdom.
Hard work builds character and homework is good for your soul.