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