Modeling is about creating a representational artifact of the real thing. For example, in the car manufacturing industry “models” are static versions of concept vehicles. These models are responsible of presenting a concept in greater detail. 3d models allow architects, engineers and product designers visualize inventions and goods. Interface Models allow for user feedback and are cheaper) to produce compared to the actual end product (the car). The process of modeling begins with a concept and results into a series of visible mockups or interactive pages that represent the solution to the problem you are targeting.
To understand models in the context you are going to keep these things in mind:

Modeling is not prototyping.
Modeling is a representation of the real thing.
A Model is a referential point to guide implementation.
A Model should be self explanatory.

TIP: Once you have a design concept in mind to communicate and propose, create a model to validate your idea, collect feedback and move into production.