I had a quick course of database few years ago and I forgot a lot from there. So you can say I'm starting from zero. I will try to explain to you on what I want to do and a picture with what I did so far.
We have a small business at home to change tires on a car (winter tires, summer tires). When I customer comes and changes tires they usually left them in our shop and we store them on a shelfs in the basement. For easier explanation let's say we have only 5 shelfs labeled from A1 - A5.
The guy comes to change from winter to summer tires. A receptor takes his name, address, car model, tires specification (of winter tires). Summer tires comes on the car, and the winter tires goes into the basement and on the shelf (let's say they go on location A1). After they are placed on the location we update the database with the location of the tire. When he comes next year we do a SQL query to see where he has his winter tires and we change them.
After receptor makes a paper with his information (name, tires, etc.) she prints this list with QR code on it with his client it. The paper goes with tires to basement and when a worker puts the on a shelf, he scans QR code on the list and QR code of location (a1 shelf) and update the database with location information of where tires are being stored.
I hope you see what I'm trying to make.
Here is the link of the ERD I made so far:
Can you please take a look and maybe suggest if anything needs to be changed.