As you gain levels your experience with your profession is also assumed to be increasing. This takes the form of 5 distinct tiers of ability gained at certain character levels. These tiers are Amateur, Novice, Practiced, Expert, and Legendary.
Primary Profession:
Level 2: Amateur
Level 5: Novice
Level 10: Practiced
Level 14: Expert
Level 18: Legendary
Secondary Profession:
Level 8: Amateur
Level 12: Novice
Level 16: Practiced
As you go up the tiers you will be able to attempt more difficult tasks and the tasks you could do already will become easier. You can choose to directly profit from your profession or work towards a specific goal. When you work towards a goal you roll a Profession Progress check. Each task you choose requires a GP value that's filled by the amount you rolled. If you exceed the amount needed the excess can be used on another task, if you are short you'll have to wait until your next session break to continue progressing.
For example: a weaponsmith might choose to make a sword worth 250GP. As an Amateur averaging 33 GP per session it might take him about 8 sessions to make it, but a Legendary weaponsmith, averaging 570GP, could make 2 easily and have started into another.
Professions:
Animal Handling
Farmer – Train mounts and war beasts, enabling their use and tweaking stats
Arcana
Spell Research – Create new spells, modify existing ones, write scrolls more easily.
Artificer – Create Magic Items and constructs from materials in the world.
Alchemist – Create alchemical brews and potions
Deception
Forger – Forge documents like shipping manifests, writs, etc. Profit and gain leverage at a risk
Investigation
Investigator – Gain intelligence on people, places, and things.
Religion
Priest – Work to gain followers for your god and spread your beliefs.
Medicine
Healer – Produce poultices, splints, and medications from herbs and other materials to help against disease and permanent injuries.
Poison-maker – Create poisons from herbs and other materials.
Nature
Herbalist - Properly identify and prepare herbs for medicines and poisons.
Farmer - Gather seeds, plant crops, and grow them for profit.
Performance
Performer - Earn money and fans, as well as possible connections with important people
Survival
Hunter – Hunt and trap animals for profit and learn to extract valuable components used in alchemy, medicine, etc.
Other:
Construction – Earn profit that increases when used directly for building.
Shipbuilding - Build custom ships and earn profit
Smithing - Craft weapons, armor, and items
Shipbuilding - Build custom ships and earn profit
Smithing - Craft weapons, armor, and items