Thanks to that your characters will be able to store 3 Source Points. However, with your progress in the story you will be able to unlock the second and the third socket. Remember that, in the beginning of the game, your characters have access to only one Source Point - this means that some of the abilities won't be available and you will have to regenerate that point after each use. One container can be found in Vault of Braccus Rex and one near Siva's House.

Regenerating points thanks to containers with substance.

Originally harnessed by the Eternals, the precursor race to the seven races: dwarves. Absorbing a spot gives you 1 Source Point and a spot itself can re-appear in the same place after some time. Source is the world energy of Rivellon, from which magic is born. You can find them scattered around the world, usually in places that are key to the story.

Regenerating points from special spots.

Absorbing a soul gives you 1 Source Point. Their location and a way of acquiring a soul can be found in descriptions of 'Withermoore's Soul Jar' and 'Vault of Braccus Rex' quests. Each use of this ability allows you to get 1 Source Point. You can use this ability thanks to two items - Purging Wand (the way of getting that item can be found in the description of 'Call to Arms' quest) and Corrupted Tyrant's Helm (check out 'How to get and use Braccus Rex's armor').

Using Purge ability (previously known as Source Vampirism).

The game offers you a few ways of doing that: When you get rid of the Collar, you can now start gathering these points. Spots like this, that allow you to restore Source Points, are plentiful in the game.

How to get source divinity 2