We can add several polynomials together, by combining the like terms.

For example: Add    

(2x² + 6y + 3xy)  ,   (3x² - 5xy - x)   and   (6xy + 5)

First, put all the like terms together:

(2x² + 3x²)+ (3xy - 5xy) + 6xy - x + 6y + 5 = 5x² + 4xy - x + 6y + 5