1. The reasons are: to greet someone, to show that you agree on something, to congratulate someone for doing well in exams and in a competition. 

Fragment w tekście: "(...) but it is used by many people from many countries as a greeting, to show they agree on something or to congratulate someone for doing well in exams or in a competition." - (...) ale jest wykorzystywany przez wiele ludzi z wielu krajów do witania się, do pokazania, że się z kimś zgadzasz lub, aby pogratulować dobrego wyniku z egzaminu lub zawodów.