A Combatant is a well-trained fighter: skilled with any weapons, capable of mounted combat and able to fight while doning armor without tiring.

As a general rule, actions in combat are resolved by rolling 2d6 (or 1d6 if the action involves higher risk and reward), then consulting the Oracle (relevant bits reproduced here):

Getting a No when you're attacked means a hit was scored against you and you must save vs Death. For the common man, failing this save means death or a dire wound. For the Combatant, though, it means only being put into an unfavourable situation: you were disarmed, was tripped and fell, was blinded or dazed, etc.

A Combatant only dies from a failed save vs Death caused by a hit if they're already in disadvantage, if they're vulnerable or unaware, or if their opponent is exploiting a weakness. In any other case, they save to avoid those things from happening. The players and the referee should discuss each situation and determine when a save vs Death should be lethal or not to the Combatant before the saving throw is made.

Given the situation allows it, a Combatant carrying a shield can interpose it against a hit that would make them save vs Death to avoid having to save. Doing so splinters the shield, rendering it unusable.