Combat Mechanics

Combat in Nyra is built for a balance of realism and very powerful late game characters. Without an attention to detail, combat can lead very precipitously to character death. The damage output of weapons has been at least fundamentally linked to what a real life version of that weapon would do in equivalence to hit point damage.
There are many different approaches to combat in Nyra, broadly characterized by the different classes. For example, while Warrior generally engages in combat in melee range, Hunters mostly stay at a distance. Mages have a variable type of engagement, largely staying at a distance, but with some spells which bring them close to their targets. Savants generally spend their combat phases giving commands and controlling NPCs. While the Brawler usually wades into combat and controls the battlefield, the Rogue tends toward stealth hit and run tactics. Further, each of these classes can be played uniquely, offering a huge variety in how combat can function for different players.
However, there are some key things held in common. First is that all of these classes typically have one skill or group of skills which they roll against in order to determine the outcome of tests in combat. For example; for Warriors, Rogues, Brawlers, Hunters, and even Savants, the skill that they attack their enemy with is generally called a weapon skill (Swords, Axes, Unarmed, Archery), whereas for the Mage this would be their magic skill. There are a huge variety of approaches that arise from the combination of feats, skill perks, and weapon choices within the game, so we can only offer a general overview.
Firstly, how does combat begin?