Editing M&M Revised (v1.5) System Resource Document (section)

===Skill Basics===  
Skills are learned abilities acquired through a combination of training (the
skill) and natural talent (an ability score). Each skill has a rank, used as a
bonus to the die roll when using the skill. To use a skill roll:
d20 + skill rank + ability modifier +
miscellaneous modifiers
The higher the roll, the better the result. You’re usually looking for a total
that equals or exceeds a particular Difficulty Class (DC) or another character’s
check total.
• Skill Rank: Your rank in a skill is based on the number of points you
have invested in skills. If you have ranks in a skill you’re considered
trained in that skill. You can use some skills even if you don’t have
any ranks in them, known as using a skill untrained.
• Ability Modifier: Each skill has a key ability, the ability modifier
applied to the skill’s checks. Each skill’s key ability is noted in its
description and on the Skills table (see page 41).
• Miscellaneous Modifiers: Miscellaneous modifiers to skill checks
include situational modifiers for favorable or unfavorable conditions,
bonuses from feats or powers, or penalties for not having proper
tools, among others.
ACQUIRING SKILLS
Characters gain skill ranks by spending power points: 4 skill ranks per
power point. Skill ranks do not all need to be assigned to the same skill.
Characters can perform some tasks without any training, using only raw
talent (as defined by their ability scores), but skilled characters are better
at such things. Characters with the right skills and feats (see Chapter 4)
can even hold their own against super-powered opponents.
Skill Cost = 1 power point per 4 skill ranks.