Should i count average of four years of high school or it is only my last grade?
All four years.
For what purpose?
For application.
For example some universities have average gpa for admissions. I wanted to know if it is 4 year gpa or only senior year.
4 years
Are you a senior in high school now, or have you been out of highschool and have a 4 year GPAs? Many kids applying to college right now may not have senior year grades yet. In that case GPA would be for last three years
Also in some states, some schools, freshman gpa not included. CA state schools an example.
Your GC also needs to enter gpa. Why not speak with him/her? The two numbers should be the same or roughly so.
And do you know if graduation exams grades count?
Are you Canadian? Only Canada puts an emphasis on Grade 12 grades. US schools look at all 4 years.
I am from Armenia and we have 3 final exams. Do their grades play any role?
What ever is on the transcript that you school submits will be considered.