Step 1: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrrr} & x^2 & 2x & 5 \\ \color{red}{ - } & -2x^2 & & 6 \\ \hline \end{array} $$Step 2: Change ALL the signs in the second row.
$$ \begin{array}{lrrr} & x^2 & 2x & 5 \\ \color{red}{ - } & 2x^2 & & -6 \\ \hline \end{array} $$Step 3: Combine like terms (add each column):
$$ \begin{array}{lrrr} & x^2 & 2x & 5 \\ \color{red}{ - } & 2x^2 & & -6 \\ \hline & -x^2 & 2x & 11 \end{array} $$