Trouble with hash.each

NEVER use puts in Rails, it causes havoc as you are sending data to the current out Which may or may not be the browser, a log file or the console

Plus you are already sending output to the browser because you are using an opening erb tag with an = sign (<%=) which essentially translates into English as 'Get the text from this ruby code and convert it into an HTML string'

You could do the following

<% h = { "a" => 100, "b" => 200 }%>
<%  h.each do |key, value| %>
   <%= "#{key} is #{value}, "}%>
<%end%>

But  the really glaringly obvious mistake is that you are thinking this code belongs anywhere near the view in the first place.
The definition of h is business logic and could change at any time so it firmly belongs in the middle tier. If there is not a logical model that ths code fits then make a module or a class
something like
h.rb

  class H
    def self.get_hash
      { "a" => 100, "b" => 200 }
    end
  end

Then in your controller action or in a view helper module you can just call @h = H.get_hash
The use the @h instance variable to loop through the results in your view

Hope that helps