когато

In a sentence

• Когато бях малък, играех в парка.

  When I was little, I used to play in the park.

  In this sentence, 'Когато' introduces a time-related clause describing the condition or context under which the action occurred: specifically, the time frame of being little.

• Звънни ми, когато пристигнеш.

  Call me when you arrive.

  Here, 'когато' introduces a subordinate clause describing the future time at which the action of calling should occur.

• Тя пее, когато е щастлива.

  She sings when she is happy.

  In this case, 'когато' is used to indicate the recurring condition under which the main action takes place: specifically, when she feels happiness.