how do i turn on vision hud?

[Ashenslinky]

when i turn my head i wanna still be able to lock on and fire

[G.J.S]

To the right of the cockpit main panel - you will see a dial called "HMD", turn it up. 

 

 

And I would also suggest reading the manual. 

[WOPR]

Do the alignment after you turn it on.