Hello and Welcome!
Mystery shopping is certainly a valid way to do that. Depending on what you want to do, ability to travel, etc., you can, once established, pull in several thousand dollars in a month and/or have many of your regular expenses reimbursed. There is a huge range of potential, depending on what your goals are.
I do suggest checking out the "New Shoppers" area of this forum first as it will really give you a great overview of the mystery shopping world. Thereafter, you should check out the huge list of companies linked at the bottom of this page. You'll eventually want to register with all of them. Of course, feel free to ask questions on this forum.
Good luck!
Hard work builds character and homework is good for your soul.