When interacting with a system, there are two types of knowledge the user may have/gain with regular use of the system. They may know exactly how the system works, or they may know how they need to interact with the system... or both!
For example, an expert in computers may know exactly how they work and all the components they are comprised of as well as how to use one. This would mean they have a deep or strong mental model of how computers work, as well as a deep or strong mental model of how to use a computer.
On the other hand, grandma may have a good mental model of how to use a computer because she is able to turn it on an play solitaire, however she would have a weak or poor mental model of how computers work because she has no experience in working with the physical structure of a computer.
