there's a location guide here, making friends and proposing there is the same as in the first town, just some of them have different items in the shop and a different activity or game you can do there
If you want to know how to unlock the places click here and follow the steps for each location.
Marrying/proposing happense when you either visit the locations and meeting other tamagotchis or by connecting your device with the app.
If you are willing to marry a specific character in a certain location make sure you visit that place a lot and taking the other character favorite item/toy. Click here for the chacaters favorite items. If you also need more tips and information visit TamaTown which is a fan site made to help tamagotchi owners.