[tasmith2009]

I have a Custom Auto sound 100watt Radio receiver and i was wondering if i get subs and speakers if i would have to get a new reciever?

[EagleAutosports]

Hiya, welcome to the site.
You probably won't need a new receiver, just wire the new speakers and subs into the output wires they should work.

[Ian1994 3.8L V6]

probably an amp would be good too. depends on how many watts your sub is and how much you want to put to it.