Skill time
Some skill checks are instantaneous. That is, used during combat, they cost no Action Points (The Combat chapter gives a brief overview of how to use AP in combat). The skills that take no time to perform include Discern (sometimes), Focus, Lore, Perception, and Vitality. Some skills are used as part of another action in combat. Some skills have AP costs inherently. A few can take days or weeks.
Take 5
On skill checks that carry no penalties for failure (see the Retries portion of the skill description) and your character is in no immediate danger, you can choose to take 5 instead of rolling. This is useful if a low roll might result in not meeting the DL, whilst a high score might not benefit anything, but something in the middle would probably work.
Take the Best
On skill checks that carry no penalties for failure and your character is in no immediate danger, you can choose to take 10 as if you had rolled it. (This does not count as a critical). As opposed to "Taking 5", taking the best requires far more time. In game terms, your character keeps trying until the check is done perfectly. Usually, this means taking the time it might normally take for one attempt and multiplying by 10 or more.