GPA = Grade Point Average. Your average grade (mark) in your undergraduate courses. In the US this is on a scale of 0 to 4.00. Your country likely uses a different scale, in which case your average will be converted to the US equivalent by the graduate schools you are applying to, or maybe by your own university.
GRE =
Graduate Record Examination. Most or all graduate schools in the US require applicants to take it. This is a general test of verbal and mathematical ability.
PGRE = "Physics GRE" =
GRE Subject Test in physics. Most graduate physics departments in the US require applicants to take it. That is, you need to take both the general exam and the physics exam.
If English is not your native language, you probably also need to take the TOEFL (Test of English as a Foreign Language) or something similar, to convince schools that you know enough English to do OK in your classwork etc.