Car audio Knuconceptz o/4 gauge wire reducer please answerrrrr important?

ok so i bought a knuconceptz 0/4gauge wire reducer so i can put my 0 gauge in and plug it to my amp. but my dad said i cant do it because its not suppose to go in your amp its suppose to go in ure battery...is tht true??? can i use the reducer???..i really want to use a 0 gauge wire... please andswer and please do not make it complicated.