Modeling helps you understand and communicate how a system works.
Systems can be complicated. Walking in a new city without your phone is sure to get you lost.
A map helps you find your destination and figure out how to get there.
Modeling is an exercise for describing the system parts and relationships. This can go further to define actual classes and tables in the system.
Unified Markup Language (UML)
Entity Relation Diagrams (ERD)
Level