(19x^2+11x+5) - (-5x^2-6x-6)
which can be written as follows
19x^2 + 11x + 5 + 5x^2 + 6x +6
The -5x^2-6x-6 is all positive because you're multiplying by negative and negative times negative is positive.
Now you can only add/subtract coefficients with similar power meaning coefficient of x^2 can only be added/subbtracted with another coefficient with x^2 term. So if you group above equation with similar coefficient it will look like following.
= (19x^2 + 5x^2) + (11x + 6x) + (5 + 6)
= (19+5) x^2 + (11+6) x + (5+6)
= 24 x^2 + 17x + 11
To answer your second question, you need to divide first the polynomial by the second polynomial. The answer will be some polynomial. There are several ways to divide polynomials. One of them is to use long division. First you need to factor both polynomials and cancel out similar terms and then use long division to divide rest. Here's the site that explains it in detail or just google long division for more info.
http://campus.northpark.edu/math/PreCalculus/Algebraic/Polynomial/Factoring/index.html
http://en.wikipedia.org/wiki/Polynomial_long_division