From the White Wolf Wiki, the most complete White Wolf reference

A Contract is a power that allows creatures of Faerie to affect the mortal world. Contracts are ancient agreements made between the Fae and living embodiments of the natural world; as with most such magics (like the Mask), these bargains extend to all creatures touched by Faerie, and thus may be learned and used by Changelings.

Each Contract is a collection of related powers, or clauses, which were agreed upon in the same bargain. Usually a Changeling must use Glamour to empower the use of most clauses, but every clause has a "Catch", a loophole in the original agreement which allows use of the power without the magical price having to be paid.

Changelings have an affinity for a number of common Contracts, which they find easier to learn than others:

• Dream - powers which enhance a Changeling's ability to interact with the dreams of mortals, and also to sense and understand the Hedge.
• Hearth - blessings and curses of good or bad fortune, these powers draw on the Fae's ancient connection to Fate. This Contract is unique in that it has no Catches; the powers must always be infused with Glamour, and always work as intended, but each has a Ban which prevents them from being used too often.
• Mirror - powers of shapeshifting and disguise.
• Smoke - powers of stealth and misdirection.

Each Seeming also has an affinity for a Contract which grants powers associated with that Seeming:

• Artifice - the Wizened's ability to create, repair and destroy all manner of manufactured objects.
• Darkness - these powers, which invoke ancient nightmares of the dark, make the Darklings truly feared.
• Elements - Elementals learn this Contract to gain protection from and control over their chosen element.
• Fang and Talon - grants a Beast the abilities of a chosen type of animal.
• Stone - the physical power and fortitude for which Ogres are famous.
• Vainglory - powers of persuasion and emotional control, known best by the Fairest.

Changelings who belong to a seasonal Court also have an affinity to further two Contracts associated with their season: the "Fleeting" Contracts deal with manipulation of the Court's dominant emotion, while the "Eternal" Contracts invoke physical manifestations of the season itself. Due to the mystical connection granted by a Court's Mantle, the more advanced clauses of these Contracts may only be learned by Changeling's with a strong Mantle for the appropriate Court. The less powerful clauses may be taught to other Changelings, but such tutelage is generally only given to those who have proven their friendship to the Court.

• Fleeting Spring - influence over Desire
• Eternal Spring - powers of growth, renewal and fertility
• Fleeting Summer - influence over Wrath
• Eternal Summer - powers of heat, sunlight and strength
• Fleeting Autumn - influence over Fear
• Eternal Autumn - powers of decay and twilight
• Fleeting Winter - influence over Sorrow
• Eternal Winter - powers of ice, snow and death