Shield: how to create user-permission level ?

Hey guys,
I would like to ask about how to create any custom user-permission using shield (I don't know the keywords  ).
For example: 
- I have a table for brands, say it's brand A, B, C, and so on.
- I want to set the exact user, let's say 'John' have access only for brand A and C. and throws forbidden access if tries to access the other brand.

Many thanks!