What is the product of 2x plus 3 and 4x squared minus 5x plus 6

The product of something means multiplying the terms together.

(2x+3) (4x^2-5x+6)

Secondly you need to distribute the terms to each other (Think of problems like FOIL)

2x * 4x^2 + 2x(-5x) + 2x * 6 + 3 * 4x^2 + 3(-5x) + 3 * 6

Then you must take into account that some of the numbers are negative. (minus-plus rules!)

2x * 4x^2 - 2x * 5x + 2x * 6 + 3 * 4x^2 - 3 * 5x + 3 * 6

Now is the tricky part of simplifying everything. 

2x * 4x^2 = 8x^3 

2x * 5x = 10x^2

2x * 6 = 12x

3 * 4x^2 = 12x^2

3 * 5x = 15x

3 * 6 = 18

8x^3 - 10x^2 + 12x + 12x^2 - 15x + 18

Then you group like terms.

8x^3 - 10x^2 + 12x^2 - 3x + 18

8x^2 + 2x^2 - 3x + 18

The trickiest part of this is distributing all of the terms within the parentheses, once you've done that, it's smooth sailing!