Hi vindarnasson, well first and foremost, you will need to have Realms. You have if if there is a tab that is called "Minecraft Realms" under the Singleplayer and Multiplayer tabs in the main menu. If you do have that, then you will need to go into the Minecraft Realms tab, and if you do have ownership of a Realms you'll be able to hit a button called "Configure". Hit Configure, and then you will see a box that you can click and invite people. To do that just type in their Minecraft username, and they'll get a message! I hope this helps!