Hey Azhael,
You have to create a Clan in the Clan-Tab in the ingame-inventory-menue thing. The one that opens if you push the Touchpad or the Optionsbutton (depends on settings). Once you´ve created your Clan you need to go to another Player ingame, stand next to him and push Square-Button for Interaction. In the Optionwheel that shows up you can invite the other player to your clan.
Greetings Siebenhayn