Class Method vs Instance Method.rb

# Class methods are methods that are called on a class and instance methods are methods that are called on an instance of a class.

class Foo
    # Class method
    class << self
        def bar
            puts "class method"
        end
        
    end
    
    # Instance method
    def buzz
        puts "instance method"
    end

end 

boo = Foo
boo.bar

zoom = Foo.new
zoom.buzz

# output:

#   class method
#   instance method

bu = Foo.new
bu.bar
# main.rb:27:in `<main>': undefined method `bar' for #<Foo:0x007efe9b97d538> (NoMethodError)

tem = Foo
tem.buzz
# main.rb:36:in `<main>': undefined method `buzz' for Foo:Class (NoMethodError)