u/BackDry4214

So, i posted here before about recently purchasing a home and wanting to get the surround speakers going again. Well it looks like theres a coax cable going from ghe wall in the living room into the receiver area that he installed awhile ago. Is there a certain adapter or anything I need to connect a subwoofer to coax? Im a total home audio noob and dont know if they normally come coax or RCA? Also any sub recommendations around the $500 would be nice.