Combat Basics
Starting Combat
Combat begins when one member of the game (player, NPC, etc) states they are taking a hostile action against another. At this point the GM will likely call for all characters to Roll initiative.
Initiative Order: Initiative is determined by the result of a 3d6 roll plus your character's Dexterity and any other applicable modifiers. The character with the highest result acts first and the rest of the characters in the combat act in descending order from there. Initiative is rolled at the beginning of combat and remains throughout the end of combat.
The Turn
On your turn you have two actions you can take. These actions consist of things like Moving, Attacking, Casting a spell, Activating an item, etc. A typical turn usually consists of taking a Move action and an Attack action, but can just as easily be taking a Casting action and a Move action or a Move action and a Activation action. Likewise you can take two of the same actions in the same turn.
Once you have taken your two actions your turn is over and the turn progresses to the next character in the initiative order.
Dealing Damage
You deal damage with the attack action. You do this by rolling 3d6 and adding the appropriate skill bonus (Fight for melee, Shoot for ranged), and any other appropriate bonuses and compare this to the opponents defense Stat. If your attack total does not exceed the target's defense stat, your attack missed. If your attack total is greater that the target's defense, your attack was successful! On a successful hit you deal damage to your opponent equal to a roll of the weapon's damage, minus your target's Armor stat.
Armor: Armor protects you from damage once you've been hit. Armor has an AR rating, this is how much damage is deducted from the total damage dealt.
Health, Healing, and Death
As stated in the section above; any amount over your defense and not soaked by armor, decreases your health total. When you are reduced to zero health you are considered unconscious. At this point you roll a d6. This is known as the Death Die and the result of this roll is the number of rounds that it takes before you succumb to your injuries and die.
Healing: If an allied character can reach you before your Death Die ticks down to zero there are a number of ways they can save you. They can make a Cunning Skill test to stabilize you, this will leave you at zero health and unconscious, but you are no longer dying. An unconscious character cannot act, and if they are attacked at all, must roll the Death Die and resume dying. Your ally can use an item or a spell, these will not only keep you from dying, but will typically return enough health that you are no longer unconscious and may act as normal.
Death: Life is cheap and Death is a real threat in the 'verse. If a character is reduced to zero health and their Death Die ticks to zero before one of their allies can reach them, they die.
However, being a Sci-Fantasy setting, even death may not always be permanent.