2d10 + Modifiers vs. Target Number
Whenever something calls for a "roll", without specifying die size, it means this type of roll.
When a "static" is called for (usually as a Target Number), the base is 11 unless otherwise specified.
The following table gives the odds of rolling at least the number on 2d10 and an approximate conversion to 1d20.
Ability Modifier Types (and Shorthand)
Use the parentheses with the shorthand at all times.
Simple (Abil): Add the modifier of one ability score.
Coordinating (Abil/Abil): Add the best modifier of the two ability scores listed.
Inhibited (Abil-Abil): Add the worst modifier of the two ability scores listed. Functionally equivalent to "X to a maximum of Y".
Double (Abil+Abil): Add both modifiers together.
Any or all checks may have an optional addition or subtraction, always always always outside the parentheses. A (Str-3) roll adds Strength to a maximum of 3; (Str)-3 adds Strength and then subtracts three. Do not confuse the two notations. This is less important in the case of double rolls, but please keep the modifiers outside.
Ability score shorthands:
The DM may add a situational modifier to any roll. It is suggested that these modifiers do not exceed ±3.
Shouldn't be used unless necessary. Most things can be resolved with a roll vs. a static.
When Not to Roll
Whenever the result of an action is immensely important to the plotline. If it would be epic for the archer to make that shot, it simply happens.
Whenever the result of an action is in no doubt whatsoever. Poking the floor with the ten-foot pole reveals that there is a pit trap there. Pushing the gargoyle's head left reveals that it does indeed slide.
Before anything has been described.