Wounds are healed through a medical skill or supernormal power.
A Scratch is too insignificant to require a roll on a healing skill (although it might require a kiss to make it better. . . ). Scratches are usually erased after a battle, provided the characters have five or ten minutes to attend to them. An individual GM may rule otherwise, of course: they may linger on for a day or two.
A Good result on a healing skill heals all wounds one level (Hurt to healed, Very Hurt to Hurt, etc.). (Scratches do not count as a level for healing purposes.
That is, a Hurt wound that is healed one level is fully healed.) A Great result heals all wounds two levels, and a Superb result heals three levels.
Healing with realistic medical skills takes time: the success of the roll merely insures the wounds will heal, given enough rest. How long this takes depends on the technological level of the game setting, and is up to the GM. (A day per treated wound is extremely fast healing, but may be appropriate in an epic-style game. Likewise, one minute per magically healed wound is fast.) Whether or not strenuous activity before the healing period ends reopens a wound is also left up to the GM. . . .
Example: a character with three wounds (two Hurt results and one Very Hurt) is healed with a roll of Good.
After the appropriate time, the two Hurt wounds will be fully healed, while the Very Hurt wound will now be a Hurt wound (and carries a -1 modifier as such).
Otherwise, wounds heal on their own at one wound level per week of rest or longer, if the GM is being more realistic. That is, after a week of rest, an Incapacitated character becomes Very Hurt, etc. The GM may also require a successful roll against a Constitution attribute:
Fair Difficulty Level for Hurt, Good Difficulty Level for Very Hurt, and Great Difficulty Level for Incapacitated.
Failing this roll slows the healing process. Someone Near Death should take a long time to heal, even with magical or high tech healing.