From Teflpedia

All is an English universal indefinite pronoun.

All is used with plural referents; e.g. all the apples were green, or singular mass nouns, e.g. "all the water was contaminated.

All is usually not used with dual number (e.g. *All my hands were burnt); rather both is usually used instead (e.g. Both my hands were burnt).

All can have "of deletion", such that e.g. "all of the actors" = "all the actors" - but this doesn't work for pronouns "all of them" not *"all them". In this regard, it is similar to both but different from other determiners, e.g. none. A failsafe rule is to always use "of".