In Trollslayers, Professions encompass a wide range of skills and knowledges, and are essentially a shorthand that allow a character to be defined without having to list every single aspect of of that livelihood on the character sheet. If you are attempting a task, and your Profession is relevant to that task, you get a +1 modifier on your skill check, in addition to any other modifiers you might have due to Talents (see below), attribute modifiers, or any other factors in play.
Experts automatically get a Profession, and it can be pretty much anything, as long as it isn't directly related to combat or magic. Common Professions for PC's would include Woodsman, Thief, Bard, Spy, and Priest. Some Professions are less useful for adventurers, like Merchant and Jester, but their use isn't restricted. Noble would also be a Profession, but unless the GM wants to run a nobility-based game, having someone of noble blood in a group of non-nobles can be unwieldy, and will probably be forbidden.
Warriors also get a Profession, one that must be based on a martial occupation. Sample Professions for Warriors would include Barbarian, Foot Soldier, Mercenary, Borderer, Pirate, and Bandit. A Knight is also a Profession for Warriors, but for similar reasons to the Noble would also probably be restricted as a choice for PC's.
Magicians do not automatically get a Profession (some one say that the ability to use magic is their profession), but for the cost of two Talents, they can purchase either a Profession that defines how they use their magic in a social contest (i.e. Village Witch, Court Wizard), or, more commonly for PC's, they can purchase a Specialization, allowing them a bonus to a particular type of magic (i.e. Divination, Necromancy).
Paragons also do not start out with a Profession, as they are already busy trying to cram two opposing skill-sets into their head. That said, for the cost of three Talents, they can have a Profession of the type that either Warriors or Magicians might have. If they want a Profession of they type that an Expert might have, that would cost four Talents.
Where Professions are broad in scope, Talents are more narrow. Sample Talents would include Riding, First Aid, Stealth, Metalworking, Tracking, Seduction, Keen Eyesight, and Ambidexterity. Talents also cover weapon and shield skills. A particular Talent can be bought more than once, if desired. A Talent gives a +1 to a relevant task for each time it is purchased. For example, a sample character might have Dagger +1, Stealth +1, Sharp Hearing +1, Persuasion +2, Singing +1, and Strong Will +2 as their listed Talents.
Experts start out with INT/2 in Talents, Warriors and Magicians have INT/3 in Talents, and Paragons have INT/4. Humans start out with a bonus Talent.
The maximum number of Talents that a character can possess is (INT+Level) x 3/4 for Experts, (INT+Level) x 2/3 for Warriors and Magicians, and (INT+Level) x 1/2 for Paragons.
Warriors may have half their starting Talents be combat-related. Paragons may have one-third their starting Talents relate to combat, and Experts one-fourth. Magicians can not start out with combat Talents, although they may learn them as they advance in Level. The maximum number of combat Talents a Warrior may know is (INT+Level) x 1/2, a Paragon is limited to (INT+Level) x 1/3, an Expert is limited to (INT+Level) x 1/4, and a Magician is limited to (INT+Level) x 1/5 combat Talents.
The maximum level of any particular Talent is (Level+RA)/10, with RA being the Relevant Attribute for that Talent. Usually, the RA for combat skills and anything requiring manual coordination is DEX; the RA for various knowledges and lores is INT; bonuses to the five senses (i.e. Keen Eyesight, Sharp Hearing) has OBS as an RA; the RA for various social skills like Persuasion and Seduction would be PRE.
Literacy & Languages - both of these are treated as Talents, but need only be purchased once, as there is no benefit from purchasing Literacy or a particular language more than once. Literacy need only be purchased once to encompass any spoken languages the character may know.
Some characters may gain Literacy as a free Talent; this does not count against their total of starting Talents, but it does count against the maximum number of Talents a given character may learn. Magicians and Paragons (unless from a truly primitive society) gain Literacy free, as do Experts whose Professions demand the ability to read as a given (i.e. Scribes). Professions where the ability to read is quite useful, but not absolutely essentialist (i..e Bards, Merchants, most Priests) gain Literacy for free if their INT is 9 or higher. All other character gain Literacy for free if their INT is 13+, unless they are from an exceptionally primitive society.
A character starts out being able to speak their native language as a free Talent (again, this does not count against their total number of starting Talents, but it does count against the maximum number of Talents a character may eventually learn). Any other languages the character wishes to be able to speak must be purchased as separate Talents. Non-humans speak their own racial tongues, and must spend a Talent to learn the regional human tongue if they wish to converse with the local human populace.