As you progress through the game, you'll begin to come across generators more often in enemy bases. You can find a permanent spawn of a generator in the Main Mission La Carcel Del Pueblo
in San Mateo
, if you need to.
Next, make sure you by the C4
skill, and cycle through your items using left on the D-Pad until you have it selected. Sneak into the base, open the gate to the generator, throw the C4 on the generator and then explode it to earn the achievement.