In layman’s terms, you either use it as an action in a greater Firefight or you use the close combat rules to resolve conflicts in a single roll outside of Firefight.
Honestly, there is no “melee combat” in this game. There’s no “sword on sword” swirling duels. It just plays out differently.
In the last session I ran, I was losing this Firefight to capture the enemy commander. I used the Close Combat action as a desperation ploy. It cost me the fight, but I got a shot at the enemy commander. He was a Kerrn, complete with Kerrn Sword. I was in iron and I just chucked a SCArE grenade at him. He won the versus test and took a chunk out of me – my grenade ripped apart the bulkhead behind him, but did not real damage.
He escaped, but because of my ploy, I captured his second in command.
That was one action in the larger Firefight. It was two rolls for me: Close Combat Unit Action plus the Grenade Individual Action. Three rolls for Rich: Unit Action, Individual Action and the Die of Fate to knock my block off.
-Luke