"Rotating" an array means taking something off the front and add it to the back. Thus, rotating the array [1,2,3] would result in [2,3,1]. Ruby already provides something for taking from the front of an array (the shift method) and something for adding to the back of an array (the push method), so all you have to do is stick them together.
irb(main):001:0> a = [1,2,3] => [1, 2, 3] irb(main):002:0> a.push a.shift => [2, 3, 1] irb(main):003:0>
Put these together in the Array class, and you'll be able to rotate any array easily.
class Array def rotate push shift end end