You may think a MMORPG that gives you control of your own self-contained party of tanks, healers, and DPS would be one where you wouldn't have any reason to group up or even be social.
You couldn't be more wrong.
The main storyquest line is a long and ardous chain which is designed to be soloed. Indeed, the bosses you will encounter in this chain can't be fought in groups. But, eventually, you will find yourself with good reasons to venture into the Shadow Dungeons which are instances meant to be tackled in a group. Even though you can control a maximum of 9 characters, wandering monsters will join a fight in progress and you could see yourself in a 9 vs. 27 if you are particularly unlucky. Shadow Dungeons seem to have automatic adds as I've yet to see a fight in there where it was just 9 vs. 9. So grouping for those is the way to go unless you have gold to burn on Bewitching scrolls. Group battles can be really dynamic as it is possible to cross-buff and cross-heal between the different groups. Finding a group is particularly easy due to a Peer chat channel that only reaches those in the same level range as you. This filters out a lot of extraneous info and insures you get level-appropriate advice.
There are also many reasons to join a good guild as soon as possible. Each character has a hotbar that can be equipped with a potion or scroll they can activate with the appropriate function key. F1 and F2 are standard but the F3 key is only available to those who belong to a guild. F4 and F5 is unlocked when your guild controls a city. Monster and craft info can be freely traded between guildies and you gain access to the private guild dungeons and training center. Training centers are a low-level training ground for guild dungeons and are a great option for those guilds that don't have a lot of high-levels needed to run a GD. Guild dungeons are timed levels where you must clear out the different floors and finally the boss for your fat loots. Groups are capped at 3 players per but you can bring as many players and groups as you like for fast and easy runs. There are also Nation dungeons available for those guilds that belong in a Nation. Those high-levels that want to run instances apart from their guild or nation can run Independent Dungeons. Eventually, Nations will want to engage in war against another Nation and group combat takes another interesting twist with open PK 3v3 groups.
One thing to note is that there is absolutely no punishment for grouping in this game and you gain the benefits of grouping (in the form of extra XP) even when the group members are separated by geography and levels. This is known as Long Distance Grouping or LDP for short.