di box is a separate box with an xlr out to run into the pa like what's on the back of your amp. it's not a bad idea to have one, but i ran for 25 years as a pro bassist without owning one. every gig with pa i ever played they had a di or mic for me anyway. so if you don't want to spend any more money, you're set. overdrive is really the only necessary effect for bass, and on some gigs you don't even need that, so you can coast for a while with just the boss if you want.
thanks for the explanation. and yeah, I do believe I've seen the PA system owners with DI boxes so it doesnt seem like a necessity to me now that I know what it is.