This number is so astronomically large that it is beyond human comprehension.
Let's start with the number 3.
Now, lets do 3^3.
That is 27.
Now, lets do 3^27
Thats 7.12 trillion
Now, lets do 3 ^ 7.12 trillion
Thats 3*3*3*3*3......7.12 trillion times
There is not a single supercomputer in the entire world that can do that calculation in a resonable amount of time.
Lets call that last calculation, 3*3*3*3*3......7.12 trillion times, G1
So we know that G1 is an enormous number.
Now we do 3^G1
And we call that G2.
Next we do 3^G2
And we call that G3.
We repeat this process of enormous, exponential growth until we reach G64
And G64 is Graham's number.