Non-english first language speaker wants to know, what does ship`s complement really mean? Most ships can have guns, but only some ships have "gunner" listed i ship`s complement and even though they have nav-computers and hyperdrives, not all have navigators. So I assume that some big ships need those roles and a little extra crew to opperate all stations, is that it? Or does it just describe what the usual crew is?

Can you fire the guns from the pilot seat or cockpit in ships with "gunner(s)" listed in complement? What about navigators?

Manufacturer's recommendation. Also, it might depend on the specific class and what it's original purpose is (the difference between and armed transport and a light freighter, for example), but I'd have to compare the different ones to give a better analysis. And you also have to consider the intended purpose of the class against what it's being used for. Some freighters have a loadmaster position. If the party isn't using a freighter for cargo transport, then they probably don't need a dedicated loadmaster; there are other examples.

The way I do it is if it's a turret (unless it's a chin-mounted turret) then it requires a crewman to man the turret. Most of the smaller freighters that have turrets have a crew complement that can run all the guns if needed; and if you add passengers they could run the other systems so the copilot, or the engineer, or whatever other crewman can do their particular job. Any (or most) forward mounted, non-turret weapons can be fired from the cockpit.

Ships complement entails what is required for the ship to be fully operational in my mind. A skeleton crew can operate it with reduced functionality.

Ships complement entails what is required for the ship to be fully operational in my mind. A skeleton crew can operate it with reduced functionality.

Actually, Strongholds of Resistance does have recommendations for running capital ships on a skeleton crew.