Skills advance the capabilities of a party member. There are three types of skills:
• Weapon Skills enable and improve the party member’s handling of different kinds of melee and ranged weapons.
• Miscellaneous Skills increase various character stats or enable and improve fighting styles, abilities or the deployment of protective equipment.
• Magic Skills allow access to spells of the seven magic schools and improve their power.
Every skill in the game has four different ranks: Novice, Expert, Master and Grand Master. Every rank provides a cumulative bonus to the effect of the skill.
Levelling up a party member provides skill points that you can spend to improve the level of any skill the party member has access to until you reach the level threshold to the next skill rank. Then you have to find the corresponding teacher to unlock the next rank, before you can spend additional skill points on that skill. A teacher is not required for a party member to reach the Novice rank of a skill.
The skills a party member can learn and the skill ranks attainable depend on his/her class or his/her Paragon Class respectively. You can see the skills and spent skill points on the Skills Tab in the Spellbook Screen.