In this video, the teacher explains the difference between linear and quadratic equations and how to model different situations using each. They provide examples of linear expressions and equations, as well as quadratic expressions and equations. The teacher emphasizes that linear expressions can be evaluated, while quadratic expressions can only be evaluated if the variable is known. They also highlight that linear equations can be solved, while quadratic equations can be solved using methods like factoring. Overall, the video aims to help students understand and identify the appropriate equations for different scenarios.