There are 3 skill trees to choose from with any class. A Guardian has Defense, Vigilance and Focus. Most PVP/DPS Guardians choose Focus for their primary points. Tank specced choose Defense/Vigilance (combination will vary). And PVE/DPS will use Vigilance/Focus.
I am not entirely clear on how to change the Datacrons, but I am sure there is a guide out there. As a Guardian, you want STR + END, how to change those in the Matrix, I do not know.