The book states that a player using the Assist Manoeuver grants a Blue die to an ENGAGED character.

Does that mean a character engaged in Melee? Or can this provide a boost to ranged attacks?

It means you need to be within Engaged range of the character being assisted in order to provide assistance.

While generally meant for the vast multitude of other far more interesting things you can do, you could conceivably use this for boosting ranged attacks given plausible narrative explanation (which shouldn't be hard).

Yep, in other words, "a character can assist an ally with whom he is engaged." But that sounds weird. Hence, the wording of the rules.

The book states that a player using the Assist Manoeuver grants a Blue die to an ENGAGED character.

Does that mean a character engaged in Melee? Or can this provide a boost to ranged attacks?

Everything. You're holding the light while whomever...picks the lock, disarms the bomb, fixes the broken terminal, etc. You're holding the IV bag while Doc patches up someone shot up, etc.

Allan Quartermain: Aim.

Tom Sawyer: That's easy.

Allan Quartermain: Adjust for wind and target movement.

Tom Sawyer: That's easy, too.

Allan Quartermain: Here's the part that's not. You have to feel the shot. Take your time with it. You have all the time you need. All the time in the world.

Yep, in other words, "a character can assist an ally with whom he is engaged."

So romantic. [sigh]

Yep, in other words, "a character can assist an ally with whom he is engaged."

So romantic. [sigh]

Player: "I'd like to assist my ally."

GM: "I don't see no ring on that finger!"