To add polynomials, simply add any like terms together ... so what is a like term?
Like Terms are terms whose variables (and their exponents such as the 2 in x2) are the same.
In other words, terms that are "like" each other.
To subtract Polynomials, first reverse the sign of each term we are subtracting (in other words turn "+" into "-", and "-" into "+"), then add as usual.