Aspects
Aspects are one of the defining features of Fate. Virtually everything of note in the game will have one or more associated Aspects. From a storytelling perspective, these function as quick, descriptive tags that sum up and differentiate characters, objects, and even scenes. These are not standardized, and can come in varying degrees of specificity. A tavern scene might simply be Crowded, or it might be Full of Music and Chatter. Aside from the obvious storytelling differences to these two aspects, they can have different mechanical effects. Aspects do not need to be exhaustive, and not everything needs an aspect. A group of nameless NPCs harassing the player characters may all fall under the aspect Angry Mob rather than being handled as individuals. A character's armor might simply exist without an associated aspect, while their heirloom sword, passed down in their family through a century of martial tradition, might have the aspect Century of Nicks and Sharpenings.
Mechanically, aspects are used by players and the GM for a number of purposes. The most typical use of aspects is for invokes. When a player or the GM invokes an aspect, they (generally at the cost of a Fate Point) are asserting that the particular aspect allows them to influence the scene. A character trying to lose themselves from pursuit into a busy tavern could invoke the tavern's Crowded aspect to boost a Stealth roll, or allow for a reroll of a low Stealth roll to achieve success. The GM could similarly invoke the tavern's Full of Music and Chatter to boost an NPC's own Stealth roll, asserting that the noise of the scene makes it harder for a player character to use Notice to listen in on a conversation.
Character Creation
The sections below list out the steps of creating a new character in Fate Core.
High Concept
High Concept: A brief phrase that sums up who a character is, and what, from the broadest picture, they might be capable of.
Example: D has realized that no one, in an entire party of 8 other players, has created a healer. Realizing that by playing a healing class character he's going to be keeping literally everyone else alive, he starts to come up with a character that is vital and necessary to the party, but who none of the other characters actually LIKE. He comes up with a High Concept Elf Supremacist Surgeon, names the character Tristani, and moves on.
When creating a character, it can be useful to start by writing out a brief sentence, or a few sentences, describing who the character is. From there, condense the description down into a brief phrase.