A favorite among Ambridge natives. As a transplant, I too love it. The ordering system is weird (think the soup episode of Seinfeld) and you'll never understand it if you didn't grow up with it.
Basically, just go in, tell them how many actual squares of pizza you want, then 10 minutes later they'll ask you what each topping is for each square. They'll add it all up in their heads and give you a total. You pay in cash only.
No delivery and no ordering ahead. Like I said, it's weird but the experience is worth it. The rigmarole can get old if you don't appreciate the hoops but luckily the pizza is worth it.
Enjoy!