Simplifying square roots....

Oh my goodness, for some reason I am having the most difficult time wrapping my head around this.

so let's say we are finding the square root of 180.....I would simplify it to square root of 9 times the square root of 20 in which i can simplify the 9 to a three so it would be square root of 3 times the square root of 20 but its not and even after watching the videos more than once i simply cant follow! Please help lol