At every even level each character gains a Level of Proficiency with a skill. There are certain level restrictions that prohibit you from moving up to the higher tracks, though some classes like the rogue lower the restrictions. At level no skill may be raised to Master until level 13.
Difficulty Class :
A normal task that anyone, even untrained could perform is DC 10. A task that is suited to someone who has had some training is DC 15. More difficult tasks that should not be attempted by those untrained is DC 20. Tasks that only very experienced people will be able to accomplish is a DC 25. Tasks that are nearly impossible require a DC 30. Modifiers can increase or decrease the DC required.
Athletics (Str) :
Used for climbing, swimming, jumping, or any other general purpose physical activity.
Ride (Dex) :
Riding a mount of any kind.
Notice (Wis) :
How perceptive you are. Used for looking for traps, seeing that almost invisible spider web, or spotting where an assassins arrow came from.
Track (Wis) :
More than just looking for tracks it is knowing where to look for them, or how to cover them up.
Animal lore (Int) :
Knowledge about basic animals, and even some that have become infused with magic.
Appraisal (Int) :
The ability to find an items worth, even if it is disguised as something else.
Herbal Lore (Int) :
Knowledge of various plants and their potential uses. Can also be used to identify poisons.
History (Int) :
Knowledge of the past, and major events that affected large areas.
The study of gods and religion, both new and forgotten.
Spellcraft (Int) :
This allows you to determine the various magical effects of a spell by simple visual or audio queues as well as going into detail about what an effect does through examination.
Heal (Wis) :
Anything from stitching up a wound to performing a major surgery belongs to the heal skill.
Geology (Int) :
Knowledge of the local land or water features.
Occult (Int) :
Knowledge of otherworldly creatures and places.
Sciences (Int) :
Need to know how to topple a wall, or build a pulley system to get you up the cliff? Sciences has you covered.
Intimidate (Cha) :
Being scary to get your way.
Persuasion (Int) :
The ability to use your words to turn someone to your point of view.
Disguise (Cha) :
Alter your appearance to that of another.
Thievery (Dex) :
The ability to pick locks, lift an object off someone.
Stealth (Dex) :
The ability to move silently, and hide from view.
Art (Cha) :
Your ability to draw/sculpt. When choosing art you must pick a type. Painting, Sculpting, ex.
Perform (Cha) :
Your ability to dance, sing, play music, etc.
Craft (Dex) :
Your ability to make a certain variety of items, such as blacksmithing.
Profession (Wis) :
Your training with a given set of skills, such as soldier, tailor, merchant.
Deception (Cha) :
Your skill at telling a lie and getting your target to believe them.
Your ability to read someone, or tell from a mere glance that someone might be more dangerous than they appear.