And how do I invite friends? I mean NO realm but a multiplayer world
As far as I know, you can't create a multiplayer world. You have to create a server.
In principle you have 2 options, well 2.5
You rent a server and configure MC on it (there are also free ones)
You are doing a local multiplayer (this is possible through the options in MC even if you are jointed into a world).
or 2.5. You start a local multiplayer and connect to, for example, a program like Hamachi. Then your friends can also join your server via Hamachi
PPS: There's also the completely exotic variant that you use your own PC as an MC server. There are enough tutorials on how to do this on Youtube or in Google