What is the correct way of using the aircraft call sign at first contact?

Question

PPL(A) - Private Pilot License - Communication - What is the correct way of using the aircraft call sign at first contact?

QuizVDS · Accepted Answer

Using all characters

QuizVDS · Answer

Using the first two characters only

QuizVDS · Answer

Using the last two characters only

QuizVDS · Answer

Using the first three characters only

PPL(A) EN: What is the correct way of using the aircraft call sign at first contact?