The central mechanic in FUDGE is a 7-valued range: Terrible, Poor, Mediocre, Fair, Good, Great, Superb (when this corresponds to numbers, Fair is considered 0, Good 1, Mediocre -1, etc). Skills and difficulty levels are generally expressed as one of the entries on this scale. The die roll is 4dF: that is, 4 dice each of which have an equal probability of rolling +1, 0, and -1. You sum the results and get a range in between -4 and 4 (aka Terrible-1 and Superb+1).
There are two kinds of actions in FUDGE, Unopposed and Opposed. In an Unopposed action, the player rolls 4dF and adjusts their skill by this: so if they have a Mediocre (-1) skill and get a sum of Great (+2) from the dice, they end up with a Good (-1 + +2 = +1) result. This is compared to the GM-set difficulty for the task to see if the action succeeded or not, and the degree by which it succeeded (most tasks have Fair (0) difficulty, so this'd be a success). Sometimes there can be bonuses/penalties to the roll: +1 is an okay bonus, +2 is quite good, and +3 is the largest likely to be applied.
In an Opposed action, the two people involved each roll 4dF, add their skill, and compare the results: the higher total wins by the amount of the difference. For instance, say Meg has Great (+2) skill but rolls Terrible (-3): her result is Mediocre (-1). Claude, on the other hand, has only Fair (0) skill but rolls Good (+1) [yes, I know it should be 'Well' in this case], giving him a result of Good (+1). Claude beats Meg by a degree of two, which is a pretty decent margin of success. In, say, combat, this would probably correspond to a solid but not disabling hit. Because there's a relatively limited range of ability (Terrible .. Superb), it is often a good idea to look for an edge in an Opposed action: find higher ground or distract your opponent or otherwise work out some way of getting a bonus.
Unlike most games, for both for both types of actions, the one who fails the roll narrates what actually happens, guided by the degree of success. In practice what this means is that if an unopposed action fails, the player dictates; if an unopposed action succeeds, the GM dictates; and in an opposed action, the player with the lower result dictates.
For an unopposed action, the results are guided by the degree of success roughly as follows:
For an opposed action, the degrees are somewhat wider due to the greater randomness:
Beyond the failure narration, the players can also affect the storyline by the use of Favors. Favors represent some sort of past relationship or incident which can work to the benefit of the character now, and are rated between 1 and 5 points, where more points represent a larger debt owed to the character or a more powerful debtor: a 2-point Favor might be "saved the wise men of a tribe in the eastern forests", while a 5-point Favor might be "saved the City of Eyes and Hands from certain destruction at the claws of the massed armies of the undead". Favors can be used to do any of the following things:
And that's pretty much it for in-play mechanics. For combat and other extended contests there are some more detailed rules which may be helpful, although this system involves a fair amount of player/GM fiat.
Character creation is also pretty simple. Before reading these rules it may be useful to look at some sample characters.
All skills that depend on training/experience have a default value of Poor (-2). Starting characters receive 35 points to allocate to raising skills; each point raises a skill by one level. At creation, characters are limited to at most one Superb (+3) skill and three Great (+2) skills (or no Superb (+3) skills and five Great (+2) skills). Typical skills should be about as broad as 7th Sea skills (not 7th Sea knacks).
Skills that don't depend on training/experience (usually physical ones like Running, Jumping, Dodging, Climbing Trees, Breaking Things, etc, but probably also a few general mental ones like Figuring Stuff Out or Remembering) instead default to Fair (0). They are raised as Gifts (see below for details on Gifts), and players who wish to have a worse-than-Fair score in one of them can take a disadvantage to reflect this.
In addition to skills, characters can have Gifts and Faults. Gifts are special abilities not covered by skills, and are generally binary, although in some cases it might make sense to have levels (Wealthy and Ultra-Wealthy or something). Characters purchase Gifts using character points: guidelines for determining gift cost are here (gifts generally cost 1-4 points). Gifts may be similarly modelled on 7th Sea advantages, although anything reasonable is OK by me.
Faults are things that cause problems for the character; any time this occurs, the character can restore one point to one of their Favors, assuming a point has been spent. Characters start off with one fault, and can take as many more as the player likes. Faults may be like a 7th Sea hubris or a Nobilis flaw or similar.