There are many ways to achieve this, the most common being KOH activation. In this method, KOH is mixed with your carbon precursor (usually in 2:1 or 3:1) and heated to 700 or 800 degrees C for 1-2 hrs. The solid residue is later washed with an acid to remove the remaining potassium. Other methods involve using molten salts or mixing the carbon precursor with a chemical species capable of inducing pores.

In summary, select an activating agent, mix it with your carbon precursor, and treat it at elevated temperatures under inert conditions, and later wash the carbon if needed.