block1.ruby

class Foo
  def self.class_method
    puts "This is a class method of #{self}"
  end

  def an_instance_method
    puts "This is an instance method of #{self}"
  end
end

Foo.class_method #=> "This is a class method of Foo"
Foo.new.class_method #=> undefined method `class_method' for #<Foo:0x007f83960d2228> (NoMethodError)

Foo.an_instance_method #=> undefined method `an_instance_method' for Foo:Class (NoMethodError)
Foo.new.an_instance_method #=> This is an instance method of #<Foo:0x007f80aa92d150>