i really do not understand this please help me.

First multiply each term in the first parenthesis by only the first term in the second parenthesis.

6x^{2} * 5x = 30x^{3}

-4x * 5x = -20x^{2}

11 * 5x = 55x

Next multiply each term in the first parenthesis by only the second term in the second parenthesis.

6x^{2} * -8 = -48x^{2}

-4x * -8 = 32x

11 * -8 = -88

Now add all of your like terms or the terms that have the same degrees.

x^{3}s x^{2}s xs coefficients (or no x just a number)

30x^{3} -20x^{2} 55x

+ -48x^{2} + 32x -88

30x^{3 } -68x^{2} 87x -88

So, your answer is:

30x^{3} - 68x^{2} + 87x - 88