I figured that it would mostly just be a primer on what you can do and the basic rules involved, even if you don't know all the mechanics of it, so that you can make informed combat choices and the like. I'm always going to be in favor of people learning the system because it's a really fun and interesting game, but I also wholly understand how needlessly complex it can get.
So with that in mind
Pathfinder 101 - The Absolute Basics
99% of the rolls and mechanical actions taken in the game can be described using the Core Mechanic of 1d20+bonus vs. DC or opposed check. As way of example:
Iseldra needs to climb up a tree to spy on a nearby bandit camp. Naturally this uses the Climb skill. Tenshi decides that this particular tree is somewhat tricky to climb, setting a DC or target number of 15.
Per her sheet, her total bonus to Climb checks is +8. This is derived from her skill points put into climbing, as well as her natural strength. LeaT rolls 1d20, and gets a 9. Her bonus is added to this roll, for a total of 17.
Since 17 is more than or equal to 15, she successfully climbs the tree.
Once on the limb, she needs to make a Stealth check to avoid being seen by the bandits. Her total Stealth bonus is +6, and with a 15 rolled on the 1d20, her total is 21.
The Bandits have a Perception bonus of +3. Tenshi rolls for the bandits and rolls an 11 on the die, for a total of 14.
Since Iseldra beat the bandits' roll, she is successful and remains hidden.
The vast majority of rolls fit this dynamic. Roll 1d20, add bonuses according to your sheet, get bonuses or penalties based on circumstances (proper climbing tools, pitch black night, one hand holding a sword, etc), and try to meet or beat a target number set by the GM. This is typically referred to as a <Skill> check. So if Tenshi aks Iseldra to roll Survival, you'll roll 1d20+9
Combat 101
During combat, you are given two actions. A Move and a Standard.
A move action is
-moving around the battlefield up to your speed
-drawing a weapon
-picking something up
-standing up if knocked down
and so on. Things that don't take too much attention and often move you around. If you move around while in melee range of someone, they're generally allowed to try and hit you for free. If Iseldra runs past one bandit to try and stab a different one, the guy she ignored is going to take a swing as she passes.
A special sort of move is the 5-foot step. No one can make a free attack if you move only five feet, but you cannot move any further for the rest of your turn. You can still take a move action, but can't use it to actually move.
A standard action is
-making an attack
-drinking a potion
-casting a spell
-bandaging up a fallen ally
Things that take time and effort to accomplish. These will sometimes give people a free attack if you aren't fighting back. Iseldra stopping the fight to swig a potion of healing will give the guy she's fighting a chance to stab her.
You can give up your standard to do a second move, but you can only take one standard per round.
Resolving attacks is the same method: 1d20 + your attack bonus vs. Opponent's AC (Armor Class)
Flanking your opponent (you and an ally attack him from opposite directions) gives you a bonus to all attacks.
Of Special Note for Lea and Iseldra
Both Lea and Iseldra have the ability to make two attacks in a single turn. Lea can use the Rapid Shot feat to fire twice, at a accuracy penalty. Iseldra can attack once with each weapon if using both of them. But, they can only attack twice if they take their full turn to do so. This is a full-round action. During this you cannot take a move action or move at all, except to take a 5-ft step.
So Iseldra can spend one turn moving up to a guy and attacking once. On her next turn she's already next to him, and can forfeit her movement to attack twice.
Lea's sneak attack does extra damage if two conditions are met.
1 - She is using a melee weapon or a ranged weapon within 40ft of the target
2 - The target cannot defend himself properly; he is flanked, distracted, unaware of her, etc.
If this sneak attack succeeds, she hampers her opponent by giving him -2 to AC, -2 to attacks, or halves his speed.
Iseldra has an animal companion, a wolf. The wolf acts at the same time as Iseldra and can make attacks of his/her own. Of special note is that every enemy the wolf attacks has a chance to be knocked prone. The classic combo is
1-Wolf runs around to opposite side of bad guy and attacks with +2 from flanking.
2-Bad guy falls prone
3-Iseldra stabs him while he's down, giving her huge +4 bonus to hit from prone and +2 from flanking.
Iseldra has a small amount of magic. In the morning every day, she can select 1 spell from the Level 1 Ranger spell list (https://www.d20pfsrd.com/magic/spell-lists-and-domains/spell-lists-ranger) and can cast it once during that day. Her number of spells will increase further as she levels.