Got some friends you'd like to invite to the shard? Leave a message for Raist on the forums. Make sure you include your character's name, the name of the player you are referring, or at least the account name so they know who the person is and who to give a reward to.
Players that refer other players can get a reward of their choice from one of the admins once the new player has played on the shard for at least 1 month. An admin can provide a list of available rewards once you and the player you referred are eligible for a reward. There are times throughout the year that a special promotion will be made available, it's a Referral Contest. In a 30-day period, the player that has the most referrals join the shard and stay for at least 30 days will have a custom piece of artwork added to the next shard patch and it will be given to the winning player. The contest will be announced the day before it begins on the Forum Calendar. Players will be required to give names of their referrals and their referrals must register on the forums to be counted as a referral.
There are other referral events that can happen as well, check the forums under The Expanse Shard Events to see if there are any currently going on!