Kelvin's Cairn in Dark Alliance is the main HUB of the world. Here you can prepare for and accept Missions, obtain loot from the loot chest, test your DPS in the training section or employ the services of the Merchant.
Once you finish a Mission you are automatically transported to Kelvin's Cairn, after a few seconds.
There's a Tome next to the Merchant, on the left, that you can collect here.
Kelvin's Cairn Points of interest
The reward chest that can be found in Kelvin's Cairn can be used to obtain all the loot you have been collecting during Missions. Note that when you obtain loot during Missions you only learn about the loot's rarity and type but are not able to know what you have actually obtained until you return to Kelvin's Cairn and open the Reward chest.
The only Merchant available in the game can be found in Kelvin's Cairn. His name is Kartik and he has set up shop in the area. You can interact with him to take advantage of the variety of upgrades and customizations he can offer, such as Skins, Upgrading Weapons, Armor or Consumables.
You can find the World Map in Kelvin's Cairn. From the World Map you can select the Mission you want to take on, given you fulfilled the requirements needed to access it.