Chronomancer
You simply need to unlock it with hero points (in the “training” panel). It does cost a lot of hero points though.
Then once you have unlocked at least the first item (“shield mastery” I think) you can start using it by taking the chronomancer line in the “build” panel. The chronomancer trait line has to be the third one.
How do i use this specilization , do i just buy a shield and equip it ?
You will get one shield when from unlocking reward (AP) by unlocking Chronomancer.