The Recruit Group Feature seems not to be known by many yet, despite it can be very useful. The patch notes told us there are chat commands called /recruitgroup and /recruitforce, which don't seem to work at all at the moment. What does work right now: Go to Menu -> Community -> Find Friend on this tab in the lower left bottom you see a button "Invite Chat Link". The rest of the window is just to search for people or to flag yourself as looking for a group (which can be useful as well). Choose the chat channel (eg. Legion or Find Group) and press the button. A blueish link "Recruit Group" will be inserted.
If people right-click the link they'll see a small info window about the members already in the group. If they left-click the link the owner of the group link will get a whisper with info about class and level from the applying person. In addition there are two links "Invite to Group" (self-explanatory) and "Reject Group". If you choose to reject the applying person, you'll send an automated polite whisper back telling him "It's a shame, but let's play together next time. Have a good time in Aion!". This can be useful to get up a group set up easy and with some info. The system is still very rudimentary tho.
Tip: As inserting the link will delete all text in the chatline, best insert the link first and then write some info behind it. Since if you do not make it clear what your group intends to do and what class/level you are searching for you'll get spammed by whispers when people just click the recruit link.
Edit: One of the recent patches changed the behavior of the links. Now if you right-click you apply for the group and a left-click shows the group window.