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