Focalisation specifies the point of view from the authorial, personal/actorial, and neutral positions. Authorial position corresponds to zero focalisation when the narrator knows more than the character. Linguistically it is represented through the grammatical peculiarity of using different tense forms and shifting between them due to the possibility of analysing events in retrospect. Personal or actorial position corresponds to internal focalisation when the narrator knows as much as the character.
It is realised linguistically through the pronouns and proper names. Internal focalisation may be fixed, variable and multiple. External focalisation is specification of point of view from the neutral position when the narrator knows less than the character. It is expressed by such linguistic markers as conjunctions of comparison, indefinite pronouns.
For more information about focalisation and its qualities, ask for expert help at http://essay.tools/essay-writer/ or find the research at https://hispabrina.qwriting.qc.cuny.edu/files/2011/06/sabz1.pdf.