Ignoreable Rules
These are rules which you could realistically never use depending on the type of game you are playing. Useful, but not 'necessary'.
More are likely to be added over time, such as underwater combat rules.
More are likely to be added over time, such as underwater combat rules.
AoEs, Cones, and Lines
This page outlines AoEs, Cones, and Lines, as well as supplying images which may help more than words.
Damage Types
This page is largely unnecessary with exception to the fact that it outlines that something which deals damage can only be up to two Damage Types at a time (with the exception of Tertiary Damage Types, which only occur if the target is vulnerable to the material of the attack such as Iron.) It also contains a table describing all Damage Types.
Falling and Momentum Damage
This page outlines what happens when you fall far enough for it to hurt, or move too fast into something (or get crushed flat).
Movement Speeds and Difficult Terrain
This page has a table describing each different type of Movement Speed, and outlines the effets of Difficult Terrain (it makes you move half as fast).
Stealth and Perception
This page is specifically and exclusively for use when something (such as a character) is (or is attempting to be) difficult to notice.