Hi, Alana! Welcome to the forum.
Since this is a new dog, you should start him off as if he isn't housetrained so that he is set up for success. Basically what that means is taking him on-leash every hour to the spot you want him to go potty at and waiting 10 minutes. If he doesn't go, go back inside. Keep him under close supervision while you are inside (where you can see him at all times, or where he is leashed to you). The moment he looks like he's going to go (sniffing around, circling, etc.), take him back outside.
Commanding him to "go potty" or other words won't help at this point if he doesn't know the command. If you want to teach a word like this, you can say the command WHILE he is doing his business, and after a week+ of doing this consistently, he should know the command. If he doesn't do the behavior when you say the command, he doesn't know it, and saying it when he doesn't know it makes it lose meaning to him.
Dogs often have set backs with big life changes (like a new family), so even if he was potty trained before, it's good to start your dog from the beginning so that there are less accidents, he can adjust easier, and you both know what to expect of each other.
I encourage you to read the house training thread and treat him like an un-housetrained dog for the first few weeks. http://www.dogforum.com/housebreakin...-how-tos-2135/