Though there are a number of ways of solving this problem, here you're supposed to build the asterisks one line at a time. There are two loops: one that loops for each line to build, and another inside it that loops for each pair of asterisks (because it shows two at a time) on that line.
Look at it this way:
Code:
Line 1 has 1 pair of asterisks:
Add the first pair.
Line 2 has 2 pairs of asterisks:
Add the first pair.
Add the second pair.
Line 3 has 3 pairs of asterisks:
Add the first pair.
Add the second pair.
Add the third pair.
Line 4 has 4 pairs of asterisks.
Add the first pair.
Add the second pair.
Add the third pair.
Add the fourth pair.
Line 5 has 5 pairs of asterisks.
Add the first pair.
Add the second pair.
Add the third pair.
Add the fourth pair.
Add the fifth pair.
Do you see where the two loops are?
And a suggestion: try writing it with two For loops first. When that works, convert the inner loop into a Do loop.