class_and_instance_methods.rb

class Klass

	def self.derp #class method
		cats
	end

	def self.cats #class method
		puts "cats are fun!"
	end

	def foo
		bar
	end

	def bar
		puts "It's a foobar!"
	end
end

Klass.derp    #=> cats are fun!
Klass.new.foo #=> It's a foobar!