Welcome to Android Central! If they're wi-fi networks that you've connected to before and saved, then they should connect automatically. But if they're wi-fi networks that aren't saved, you have to select them. This is generally a good idea from a security standpoint, because there are some open wi-fi networks that might be used by some as a lure, and since they're not secured, an unsavory person could eavesdrop on your connection.