When rolling for a Skill, the player rolls a number of dice equal to his Skill Rank, choosing the highest roll and adding it to the Aptitude of the Attribute associated with that Skill. The character's Skill Rank is then added to this number. The result is his Skill Total for that action.
Example: Victor has a Swordsmanship of 4. He attacks, rolling a 9, an 8, a 7, and a 2. His highest roll was 9, so he adds that to his Skill of 4, then to his Agility Aptitude of 7, for a total of 20.