Basically, if you cut it in half starting from the top straight down it would make it a rectangle because it can't be a square because all sides are not equal. And if you go from the far right top edge to the bottom left edge it will still be a rectangle but long.
The greatest common factor is the largest number that both numbers can be divided by. For example, in #1, 36 and 9 can both be divided by 9 to become 4 and 1.