Evaluating expressions involves plugging in values for variables in an algebraic expression and then calculating the numerical value of the resulting expression. The steps are to 1) identify the variables, 2) substitute the given values for the variables, and 3) simplify by multiplying and adding/subtracting terms. Evaluating expressions is an important algebra skill that is used to solve many problems. Learning how to evaluate expressions will help with more advanced algebra concepts in the future.