You may want to review linear equations first.
Suppose we have an equation with a polynomial on one side and 0 on the other. For example, we could have 2x2 + x = 0. It's not obvious how to solve this. But the left-hand side factors as x(2x + 1). So the solutions of the original equation are just the solution of x = 0 and the solution of 2x + 1 = 0. These are 0 and −1 ⁄ 2. (It works because two numbers multiply to 0 exactly when one or both of them is 0.)