Using Minecraft Pocket Edition?

On McPE, you connect to another's nearby server to play on it, I'm afraid there aren't any huge servers, and you can't join long distance servers. Only people near you. There are a few apps that let you join servers on mcPE, but alas they have a server limit of four to five people, full of inexperienced people and useless.

Your server should save automatically when you exit the app.

You may play on other's nearby servers, although I don't believe you can have more than four people. Both the server's creator and joiner must be connected to Wi-Fi to do this.