FATE has a few main ideas:
- Concepts - The "basis" for your idea. A ronin exiled from his clan, a knight in an era where chivalry is dead, a gunslinger in the old west.
- Trouble - The character's failing. The ronin was too honourable, the knight is delusional and charges at windmills, the gunslinger can't say no to a pretty face.
- Aspects - Some special part of the character. The ronin has a familial blade, the knight has a trusty mount, the gunslinger is a cool hand.
- Skills - The character's abilities. The ronin has great swordsmanship but terrible talking ability, the knight is wise but incompetent in battle, the gunslinger is good at shooting and talking but can't ride a horse to save his life.
- Fate Points - Points that are used to invoke concepts, trouble or aspects.
- Stress - Your "hit points". Maximum stress is linked to certain skills. In base FATE, Physique is linked to Physical Stress and Will is linked to Mental Stress. Gaining stress gives you Consequences (which you don't want).
- Consequences - Your "injuries". When total stress hits even values (2/4/6 etc), you gain a consequence. They start out mild but increase rapidly in severity. These consequences can be anything (being shot could result in your arm being put out of action or being unable to run etc).
FATE uses d6 rolls to determine success or failure. 1 or 2 is a failure, 3 or 4 is a neutral roll and 5 or 6 is a success. Almost every roll uses 4d6 and then these are tallied and a relevant skill of the character's is added on as a result (and any relevant opposing "skills").
Where FATE gets interesting (and different) is the use of concepts, troubles and aspects. Players can spend FATE points to invoke these in themselves or others, to get additional bonus dice on rolls. As an example, the knight invokes his trusty mount to flee a situation, paying a FATE point to the GM for it. Or the gunslinger tries to ignore a woman in distress but the DM says that he'll have to give up a FATE point to do it (or the DM will pay him a FATE point if he goes in for the hook).
The interesting thing about FATE is how "open" this concept is to anything else. A storm, as an example, has the skills Cold, Rain and Sleet with the aspect "Imposing" and "Deafening". Thereby, we can apply it to the tribal idea I've mentioned above.
Keep in mind that, often, an aspect and a trouble are relatively indistinguishable, the primary difference is whether you pay to do them or whether you get paid to do them. A person can have the trouble or the aspect "cannibal", as one example. If it's a trouble, then he struggles to resist eating human flesh. If it's an aspect, then he does it as a way to gain power. Or something along those lines.