Questions & Answers about Все друзья гуляют в парке.
все (no diacritic) is plural “all” (e.g. все студенты = “all the students”).
всё (with ё) is neuter singular “everything” (e.g. всё хорошо = “everything is fine”).
гуляют is the 3rd person plural present tense of гулять (“to stroll, take a walk”). It follows the 1st-conjugation pattern:
я гуляю, ты гуляешь, он/она гуляет, мы гуляем, вы гуляете, они гуляют.
гулять implies walking as a leisure activity or strolling without a fixed destination.
идти (unidirectional) / ходить (multidirectional) focus on movement from point A to B.
After в meaning “in” (location), Russian uses the prepositional case. For most masculine nouns ending in a consonant, add -е:
парк → в парке.
As a pronoun it goes:
Nominative – все
Genitive/Accusative – всех
Dative – всем
Instrumental – всеми
Prepositional – всех