What is the difference between relational and non relational system?

Typically, a relational system works with relations and relationships among relations. A relation is just an abstract representation of a real life entity or a virtual object with properties and behaviors. For example, it can be a Car(real life) or a Bank Account(virtual). Now, these relationships are predominantly governed by Set Theory Functions and Mappings.

Where as a non relational system are more like Linked Lists and Indexes. We donot establish relations among entities there rather we see how they are arranged and linked up with one another.