Step 1: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrrrr} & 2x^7 & 4x^6 & 3x^2 & 2x \\ \color{blue}{ + } & 3x^7 & 5x^6 & 2x^2 & 6x \\ \hline \end{array} $$Step 2: Combine like terms (add each column):
$$ \begin{array}{lrrrr} & 2x^7 & 4x^6 & 3x^2 & 2x \\ \color{blue}{ + } & 3x^7 & 5x^6 & 2x^2 & 6x \\ \hline & 5x^7 & 9x^6 & 5x^2 & 8x \end{array} $$