newbie question

[Suicide Junkie]

Transports are for carrying stuff. Population is not the only item useful to have moved around, of course.

Troop Transports are great for planetary assaults.
Cargo Transports can keep a fleet supplied with extra fighters, drones and more.
Since sat and mine launchers count as cargo, they work very well on a Transport hull.

As for resupply, most mods add the ability for Supply pods to count towards your cargo restriction on transport hulls. This means you can easily build a massive tanker to shuttle supplies from a depot to the front lines.

Once you get the tech, a single Quantum Reactor will be enough to keep your fleet fully supplied forever.