There's a number of YouTube videos that introduce you to Pathfinder but be warned, the cringe is real. As such, I thought I'd put together a brief introduction to some of the basic mechanics of the game to help prepare you for our first session. Pathfinder can be pretty complex but you will only be responsible for your character. You only need to understand what applies to your character and everything else will be handled by the Dungeon Master (DM).
For our purposes, you need to decide on an idea for your character that includes their race, class, traits, and alignment. Knowing about where they are from in Dirio might be helpful but it isn't essential. Once you have decided on those details, we will meet for our first session and we can put together the rules materials of your character (generally referred to as crunch).
Pathfinder is a collaborative storytelling endeavor. As the DM, I will be your referee and primary storyteller. I will provide you with the situations that you are in and play all the other parts in the world. The innkeeper you speak with will be voiced by me and the monsters you fight will be controlled by me. You will be responsible only for your own character but your actions will dictate the direction of the story. The aim is to represent a real living breathing world in which you can talk to anyone, do anything, and try even the most outlandish ideas.
Generally, you will all be able to tell me what you would like to do and I will tell you what rolls or other rules are necessary for such an action. This general play is not turn based and players can decide who amongst each other gets to speak with the DM. There being only one of me, you will need to give me time to make decisions and let you know the results of your actions. If you end up in combat, a turn order is enforced based off of an initiative roll and you can only act on your turn.
Pathfinder uses the d20 system for most of its mechanics. As such, most rules things are decided with a twenty sided dice (d20). You roll the d20, add any relevant modifiers based on your character, and tell me your total. I will compare that total with the Difficulty Class (DC) of what you are trying to do. If you exceed the DC then you have done what you were trying to do. If you are under it, you fail to do what you are trying to do. If you are significantly under what you are trying to do, there might be a further negative consequence. I generally rule that players win on ties.
Here's an example. Bert the Gnome and Hogan the Dwarf are walking down a corridor. The DM calls for them to make a Perception skill check because there is something ahead that is difficult to see. Bert rolls a d20 and gets a 15. He has a modifier of 5 that is based off of his stats and skill ranks. As such, he adds the total of his roll (15) with his modifier (5) and tells me his total is 20. Hogan, on the other hand, rolls a 3 and has only a 3 modifier. As such, his total is 6. Without telling the players, the DM knows that the DC was 15. As such, Bert sees that there is a hiding goblin up ahead while Hogan does not. Bert is free to tell Hogan but if he doesn't Hogan will proceed forward totally unaware.
This mechanic applies for any skill check, initiative, attack roll, saving throw, or spell resistance check. When in doubt, roll a d20.
Critical Failure and Critical Success
Getting a 1 or a 20 on a d20 can have additional effects. For instance, any attack is automatically a miss if you roll a 1 and automatically a hit if you roll a 20. Be sure to mention if you rolled what is called a "natural 1" or a "natural 20" since that might have some effect on what you are trying to do.
There are some occasions where you will need to roll another type of dice, typically for the damage a weapon or spell is going to do to an enemy. These dice are referred to simply as a d- followed by the number of sides the die possesses. Normal types of dice are: d4, d6, d8, d10, d12, d20, d100.
A d100 is generally not actually a 100 sided die. Instead, there will be two ten sided dice rolled. One acts as the tens and the other as the ones.