How to convert US CGPA 3.02 to any Australia's grading system?

I can't address the Australian system, but I can give you an overview of the American system, and perhaps that will help. Generally speaking, course grades in the US are given as follows: A (best), B, C, D, or F (failed). "E" is not used. Some schools use numbers instead of alpha characters. That is, an A is equivalent to a "1", a B is equivalent to a "2" and so on.

The grades of A, B, C, and D (or 1, 2, 3, and 4) may likewise be accompanied by a "+" or a "-" to indicate performance just above, or below, that level. That is, an "A+" indicates superlative work; an "A-" or "B+" indicates work somewhere between the "A" and "B" range, and so on.

Each grade will worth a certain number of points. This chart is hypothetical:

(A+) or (1+) or (A) or (1) = 4.0 grade points (the + honorary, no additional points granted)
(A-) or (1-) or (B+) or (2+) = 3.5 grade points
(B) or (2) = 3.0 grade points
(B-) or (2-) or (C+) or (3+) = 2.5 grade points
(C) or (3) = 2.0 grade points
(C-) or (3-) or (D+) or (4+) = 1.5 grade points
(D) or (4) = 1.0 grade points
(D-) = 0.5 grade points
(F) = 0.0 grade points

(In addition, as if it's not complicated enough, some classes are listed as "Honors" classes or "AP" (Advanced Placement) classes. Some schools add an additional point to the grade points awarded for successful completion of an Honors/AP class. That is, if you received an A in an Honors/AP class, you would be awarded 5 points instead of 4; if you received a B, you would be awarded 4 points instead of 3... and so on.)

Each class is assigned a certain number of credits. (For example, a biology class may be worth 3 credits, while a physical education class may be worth only 1 credit.
(See "Source", below, to view a typical high school program and the credits assigned to each class. Please note: the number of credits awarded for each class can vary by state, or even by local school district.)

To calculate one's GPA, one multiplies the credits earned for each class by the points awarded according to the grade the student received in that class. Then, one adds the total grade points for all classes, and divides by the total number of credits. The result is the student's GPA.

For example, here is a hypothetical year of school, the credits earned, the grade points awarded, and the resulting GPA:

First Semester
Biology (4 credits) ----- (A) 4.0 points x 4 credits = 16 grade points
Algebra I (3 credits)-----(B-) 2.5 points x 3 credits = 7.5 grade points
History (3 credits) ----- (A) 4.0 points x 3 credits = 12 grade points
Art (2 credits) --------- (C) 2.0 points x 2 credits = 4 grade points
Music (1 credit) --------(B) 3.0 points x 1 = 3 grade points
English I (3 credits) ----(A-) 3.5 points x 3 = 10.5 grade points

Second Semester
Chemistry (4 credits)--- (A) 4.0 points x 4 credits = 16 grade points
Algebra II (3 credits)--- (B) 3.0 points x 3 credits = 9 grade points
French (3 credits) ----- (D+) 1.5 points x 3 credits = 4.5 grade points
Chorus (2 credits) ---- (A) 4.0 points x 2 credits = 8 grade points
English II (3 credits) ----(B) 3.0 points x 3 = 9 grade points

First Semester, the student took 16 credits and earned 53 grade points.
Second Semester, the student took 15 credits and earned 46.5 grade points.

For the year, the student took 31 credits and earned 99.5 grade points.
To calculate GPA: 99.5 grade points divided by 31 credits yields a GPA of 3.209, which rounds to 3.21.

This student's cumulative GPA, for this one year, is 3.21.

There is one more facet to this system that you may need to know. The question is, when classes are graded on a percentage basis, what percentage is necessary to earn an A, or a B, and so on? Well, there is no national, or even state, standard. For example, a 93% may result in a grade of A at one school, A- at another school, or even a B at a third school.

However, the following is one standard chart (not hypothetical) that many schools use:
...........%.......Grade points
A.....93-100.....4.00
A−....90-92......3.67
B+...87-89.......3.33
B......83-86......3.0
B−....80-82.....2.67
C+...77-79......2.33
C.....70-76.....2.0
D.....60-69.....1.0
F......0-59........0.0

Finally, when you apply to an American college or university, the admission office will evaluate your transcripts to determine whether you have met entrance requirements; they will review to see if any mandatory classes are missing, and they will convert your grade point average to the American system. Each college/university has staff members who specialize in international transcript evaluation.

Until then, you will not really know what your "American" GPA would be. But, I hope this information gives you some idea how it's done in the US...
Good luck!