Marked as Best Answer
1) Open up parentheses. If there is '+' sign in front, just drop parentheses and keep signs of all terms inside unchanged. Otherwise, if there is '-' sign in front, drop parentheses and that '-' sign and change sign of every term inside parentheses.

In your case,

(3x^{4}-2x^{3}+4x-2)+(3x^{3}-2x^{2}-x+4)=3x^{4}-2x^{3}+4x-2+3x^{3}-2x^{2}-x+4;

2) Now collect like terms, that is terms with the same powers of x. In your case those are:

-2x^{3} and 3x^{3}; 4x and -x; -2 and 4.^{
}

3x^{4}-2x^{3}+4x-2+3x^{3}-2x^{2}-x+4

Here I underlined like terms and marked them with different colors.

Combining like terms is done like this:

-2x^{3}+3x^{3}=(-2+3)*x^{3}=1*x^{3}=x^{3}.

I took common factor (x^{3} in this case) out using distributive property of multiplication.

Similarly, 4x-x=3x and -2+4=2.

So, the final result is:

**3x**^{4}+x^{3}-2x^{2}+3x+2