here's your answer:

they don't auto fire you have to guide them via turret-view mode
but there is a tip that says: let them be concetrated with your onboard "forward"
guns it'll give out a ton of damage to the unlucky fellow that you're aiming at

LOCUTUS-

WE ARE THE BORG, WE WILL ADD YOUR BIOLOGICAL AND TECHNICAL DISTINCTIVNESS TO OUR OWN, YOU WILL BE ASSIMILATED,
RESISTANCE IS FUTILE

thanks for the tip

If you want to fire behind, say while running for a second, hold down the V key and fire behind with the turret.

Turret view is cumbersome and takes a few seconds to get on target, use V, much easier.

k i now have a ship with a turret slot and will try it out

how do concentrate them with forward fire?

you don't. It's done automatically

LOCUTUS-

WE ARE THE BORG, WE WILL ADD YOUR BIOLOGICAL AND TECHNICAL DISTINCTIVNESS TO OUR OWN, YOU WILL BE ASSIMILATED,
RESISTANCE IS FUTILE

ah