първи

In a sentence

• Той беше първият, който пристигна.

  He was the first to arrive.

  Here, 'първи' is used as the ordinal number 'first' to describe sequence.

• Успях от първия опит.

  I succeeded on the first try.

  In this sentence, 'първи' describes the initial attempt, again as an ordinal reference.

• Обичам първите дни на пролетта.

  I love the first days of spring.

  Here, 'първи' is used in plural form to indicate initial days in a sequence.