Step 1: First we have to write polynomials in descending order.
$$ \begin{aligned} P(x) &= 2p^5-5p-4 \\ Q(x) &= 6p^5-p+8 \\ \end{aligned} $$Step 2: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrrr} & 2p^5 & -5p & -4 \\ \color{red}{ - } & 6p^5 & -p & 8 \\ \hline \end{array} $$Step 3: Change ALL the signs in the second row.
$$ \begin{array}{lrrr} & 2p^5 & -5p & -4 \\ \color{red}{ - } & -6p^5 & p & -8 \\ \hline \end{array} $$Step 4: Combine like terms (add each column):
$$ \begin{array}{lrrr} & 2p^5 & -5p & -4 \\ \color{red}{ - } & -6p^5 & p & -8 \\ \hline & 8p^5 & -6p & 4 \end{array} $$