I've seen them mentioned in several places, but they are skills that I haven't seen, like Iron Skin, etc. Is there anything special I have to do to get them to open up for me?

Expert skills are unlocked when an attribute (Strength, Intelligence, Piety, Vitality, Dexterity, Speed, or Senses) reaches 100.

Here is a link for some descriptions of the expert skills:

http://www.geocities.com/jandrall/Wi...8/Stats100.htm

Here is a link on what some of the expert skills give you, quantitatively that is:

http://www.geocities.com/shau185/attributes.html#expert

BTW, the descriptions of the skills are in the manual.

Here are description of the skill

And to clarify, the character's base attribute must be 100. bonuses from items or spells do not count for this purpose.

Also, several items actually give you a bonus to an expert skill. And if you don't already possess the skill, you get it at that level (eg Iron Skin 10) but it wont go up from use like a normal skill until you unlock it by getting the attribute (eg Vitality) to 100

Cool! Do they go up through use like other skills, or are expert skills purely trained?

yes, they go up like other skill.