The .each iterator just tells the do the same thing for all items in an array and other stuff you will see later. Take a look at this
odds = [1,3,5,7,9]
odds.each do |x|
print x * 2
once you click on the save and submit button ..you see all the items in array multiplied by 2 i.e. it becomes 2 6 10 14 18. The x is just trying to represent any item in the array .. it could be anything you want .. a ,N ,B...I could not open or download the picture you pasted . but ii hope this will help..