If you're new to Dark Souls 3, you've probably briefly heard the word "covenant". These factions found in the game are groups that the player can join, and by following their principles unlock special rewards, as well as affect the online aspect of the game. As you play through the game you'll be able to advance through the four ranks of each covenant and interact with other players in special ways depending on which covenant they belong to. While there are no downsides in being in a covenant, some are more interesting than others depending on your play style and what you're looking to get out of your online experience.
After defeating Darkeater Midir, you will received the covenant item. Once in this covenant, the player will be summoned to become Halflight, Spear of the Church during their boss fight.
You can also be randomly summoned to act as Halflight's defense with fortified armor, but with no capacity to use Estus Flasks to heal yourself up. If you fulfill this task you will be granted the reward of Filianore's Spear Ornament, which you can use to rank up in the covenant. Although the mechanics of this covenant are interesting, they can be a bit limiting for those seeking out a more PvP based experience.
With the Aldrich Faithfuls as your main rival, once you have learned the Darkmoon Loyalty gesture and retrieved the covenant item from Anor Londo, you can join the covenant. As a member you will be summoned to defend those in the Way of Blue covenant to defend them from invaders. If you fancy yourself a helpful and righteous type of player, this covenant, or the Blue Sentinels which is highly similar in principles and rewards, is the one for you.
Once you've obtained the covenant item from Anri of Astora or Horace the Hushed, you will be able to join this covenant. Much like the Blades of Darkmoon, your main mission is to defend those in the Way of Blue covenant from invaders. The rewards are practically the same, but within the Sentinels you do not have a rivalry with any of the other covenants. This is perfect if all you want is to defend those considered your allies from invaders and play the part of a protector.
In Irithyll of the Boreal Valley, you will come across Archdeacon McDonnell. Interacting with him will give you the covenant item, and it is to him you need to make offerings, specifically Human Dregs, if you wish to rank up in this covenant. Being a member in this covenant sets you up to be summoned to defend around the Anor Londo area, even if at the time of summoning you're nowhere near it. You also have the option to invading as a team.
If you pray to the Old Wolf of Farron in Farron Keep, you will receive the covenant item needed to join. After this, you will be summoned by players to protect against invaders, but you can also invade worlds yourself in a team.
You will only invade worlds where the the boss of an area has not yet been cleared by the world's host. The versatility this covenant provides is quite nice, with a duality of being able to protect players but also go on the offensive.
Membership to this covenant is granted thanks to Emma, who will provide you with the covenant item. This covenant is by far the most defensive of all the other ones, as it simply provides you with the protection of the Sentinels and the Blades, who you can summon to your rescue when your world gets invaded. Way of Blue is a great option for players who might be new to the game or the online aspect of Dark Souls 3 and need extra muscle to fight off those pesky invaders.
One of the more unique covenants, the covenant item is found in the Cathedral of the Deep. Once you're member, you gain the ability to be reborn in the game. This means you can change your appearance and character stats each time you choose the option.
You can also invade other worlds. Rosaria's Fingers is ideal for those who want special versatility in their game and who can't quite make up their minds about their characters. Keep in mind, however, the rebirth times are limited to five times per new game cycle.
The item to join is found in the Undead Settlement. As a member of this covenant, you will be summoned by other players to help them clear out areas or defeat bosses. Once you've completed your duty, both you and the host are awarded a Sunlight Medal, which can be used to rank up in the covenant. This covenant is the ultimate co-op experience, perfect for those who want to enjoy Dark Souls 3 with a friend, or just help a newbie or a stranger get through their game. Moreover, you'll be tempting other friends to join by granting them the Sunlight Medal at every successful mission.
Although all covenants are unique and fun in their own regard, our personal favorite is without a doubt the unpredictable covenant of Mound-Makers. Being in this covenant grants the player with most freedom, whether they invade or are summoned. They can turn on their hosts in gut-wrenching betrayal or choose to help them out of kindness. Agents of chaos, their members are summoned as invaders into worlds with most players to maximize the amount of havoc they can wreak. If you despise being chained by restrictive rules and want to carve your own independent path, Mound-Makers are the way for you to go.