You want a world location. Typically you want the world location of the impact point where the explosion hit (you may get this from collision testing/handling) but, worst case, just use the actor world location of the exploding actor.
PoolingMethod has to do with if you have tons of explosions, and want them to re-use rendering resources (and limit the max number going at the same time.)
AutoActivateSystem means it will start playing right away, you don’t have to separately call Activate on it to make it start emitting particles and animate.
WorldContextObject is the object that tells this system which world to spawn into. 99.9999% of the time, you’ll want to use the object that’s exploding, or if that’s already gone, use perhaps the player(controller) viewing the explosion.