Societys or shortly soc are communities like in other games to stay in the same Group.
In Eve-Online its called Corporation[corp], in WOW or other Games its called a Guild.
U can apply over a Society Terminal
On Rocktropia is it called Social Networker.
Hier a Picture with Society-menu.
It is better to talk at first with people from societys before u apply.
Different societys have different objectives and some socs are closed for new applicants.
A further thing, what only societys can do is, claiming PVP Land Areas[LA] , what generates Tax-income. This LA claim lasts one week , then it can be competited again.
The Tax are split by the number of Soc-members and u can receive it via the Ped-Flow center by right clicking on the Ped-Card in your inventory.
A Soc has aswell a own society-channel in the Chat.