This rule has been confusing me for some time.

Getting a Target Lock is an action. But is firing a missile a new action? (which makes it cost two rounds to actually fire of a torpedo/missile)

And if firing a missile is a spending your action is Darth Vader able to both get Target Lock and fire the missile in the same round due to his pilot ability?

Firing a missile is not an action. It is an attack. Instead of attacking with the primary weapon you attack with a secondary weapon which happens to be a missile. In order to attack with a missile you need to have a target lock (exception: deadeye) and in most cases discard the target lock (exception: homing missile).

You can target lock and fire a missile in one round.

Thanks dvor! Cleared things up for me.

Designing a squad will be simpler now

Firing a missile is not an action. It is an attack. Instead of attacking with the primary weapon you attack with a secondary weapon which happens to be a missile. In order to attack with a missile you need to have a target lock (exception: deadeye) and in most cases discard the target lock (exception: homing missile).

You can target lock and fire a missile in one round.

While technically correct, this explination leaves a lot out of the actual answer.

When you make a primary weapon attack, there are no requirements for the attack. Secondary weapons, however, have different requirements and prerequisites.

Attack (Target Lock): attacks require you to perform an attack, and the prerequisite is the (Target Lock). There are missiles that do not require a target lock (Homing Missiles), but many additional secondary weapons that do not require them either. Heavy Laser Cannons and Ion Cannons/turrets both require no other requisite to fire. Other turrets require a focus token (Blaster Turret) to fire and you must have one of those to fire.

Make sure to look at the entire header and card inserts to understand how a weapon is activated/fired.

And, of course, if you spend your target lock to fire a secondary weapon (one which requires you to 'spend a target lock' to fire it), the target lock is gone and cannot be spent to modify the results of the secondary weapon attack. New players sometimes have confusion and assume you can spend the TL to fire the weapon and still use it for the reroll function as well.

Attack (Target Lock): attacks require you to perform an attack, and the prerequisite is the (Target Lock). There are missiles that do not require a target lock (Homing Missiles), but many additional secondary weapons that do not require them either. Heavy Laser Cannons and Ion Cannons/turrets both require no other requisite to fire.

Just a note that this is not quite right, currently all missiles (including homing missiles) require a target lock; the advantage with homing missiles is that you don't need to spend the target lock to fire them, so you can still us it to modify the dice roll.

On any upgrade card the text in bold tells you how the card is activated. It will either be an "Attack" with a string of conditions or it will be an "Action" and then what happens when you take that action.

Secondary weapons are, for now, the only upgrade cards that are activated with an attack. But using a secondary weapon to attack with is always optional.