After a period of quarantine (2 to 4 weeks) to make sure he doesn't have external parasites like lice or mites, or a lurking illness, then let them see each other through a fence for a couple of days.
Then let them free range and watch the rooster. He will likely try to impress the girls so that they join his harem.
Good roosters will dance and flutter around the girls, calling to them and trying to entice them with food treats. Aggressive roosters will simply chase them down, grab them and harshly mount them with the hen screaming. Some get so aggressive they can hurt the hen. Aggressive roosters will do that all day long.
I find aggressive roosters best served with rice.
Hopefully your boy is as sweet as the previous owner says and will charm your girls lavishing them with gifts and care.
He may even get hazed a bit by the alpha hen, which is fine. He will in time charm her too.
LofMc