How does Array#sort work when a block is passed?

Question

I am having a problem understanding how array.sort{ |x,y| block } works exactly, hence how to use it?

An example from Ruby documentation:

Answer 1

<=> is a method is ruby that returns ( self.<=>( argument ) )

• -1 if self < argument
• 0 if self == argument
• 1 if self > argument

x and y are items of array. If no block is provided, the sort function uses x<=>y, otherwise the result of the block says if x should be before y.

array.sort{|x, y| some_very_complicated_method(x, y) }

Here if some_very_complicated_method(x, y) returns smth that is < 0, x is considered < than y and so on...