Assuming you want to do a cartesian product, then you basically form items (x,y) such that x is in set A, and y is in set A
More generally, A * B will consist of items of the form (x,y) such that x is in A and y is in B. However, we have B = A.
So,
A * A = {
(a,a), (a,b), (a,c)
(b,a), (b,b), (b,c)
(c,a), (c,b), (c,c)
}
I broke things up into separate rows to show that we can form a 3x3 table. Each row is a different x value from the set {a,b,c}. Each column is a different y value from the set {a,b,c}
In my opinion, this helps organize things much better than rather have it all on one single line like this
A * A = { (a,a), (a,b), (a,c), (b,a), (b,b), (b,c), (c,a), (c,b), (c,c) }
which in all honesty looks like a bit of a cluttered mess.