Basic Rules and Advanced Rules
The rules split into two halves. Basic rules apply to every model unless specifically stated otherwise -- movement, shooting, close combat, Panic tests, and so on; everything an average infantry model needs. Advanced rules apply only to specific models -- an unusual weapon, a special ability, a standard bearer or hero, or a model that isn't ordinary infantry -- and are detailed in that model's own entry in its Warhammer Armies book.
Basic Versus Advanced
An advanced rule always overrides a conflicting basic rule -- a model immune to Panic, for example, simply never takes a Panic test at all. In the same way, if a rule in a Warhammer Armies book ever conflicts with this rulebook, the Armies book takes precedence.
Uncovered Situations
If a situation genuinely isn't covered by the rules, discuss it with your opponent, and settle it with a roll of 4+ if you can't agree. Consider reporting it afterward so it can be clarified for other players in the future.