You may want to review solving quadratic equations first.
The bit of the quadratic formula inside the square root sign — b2 − 4ac — is called the discriminant. It tells you a lot about the equation you're trying to solve. If it's positive, then the equation will have two real solutions. If it's 0, then the equation will have only one solution (which will be real), since 0 has only one square root. If it's negative, then the equation will have two non-real solutions.
Furthermore, if it's positive, then we can learn something about the two real solutions by looking more closely. If it's a square, then the two solutions will both be rational. If not, then they will both be irrational (but still real).