Minecraft pe multiplayer mode permanently?

I've been playing minecraft Pocket Edition (multiplayer) together with my two friends for a long time. However, this is only possible with an invitation. That's why I ask myself whether it is possible to enter the server without an invitation and just like that alone. When my friends don't play, for example, but I can still go out into the world. That is definitely not possible but asking doesn't hurt ^^

I'm not sure but there are soapps where you can make a server.

You can do whatever I want on it

Right. I was just about to look it up, but how do I make such a server?