_form_search.html.erb

<%= form_tag search_path, method: :get do %>
        <%= text_field_tag :q, nil %>
<% end %>

application.html.erb

<%= render partial: "search/form_search" %>

index.html.erb

# una carpeta en view que diga search y dentro necesitas el index mas el partial del search_form

#lista de resultados
Productos: 
<br>
<% @products.each do ||%>
....
<br>
<% end %>
Articulos: 
<br>
<% @articles.each do ||%>
....
<br>
<% end %>
Municipios: 
<br>
<% @municipalities.each do ||%>
...
<br>
<% end %>
Empresas: 
<br>
<% @enterprises.each do ||%>
...
<br>
<% end %>
Categorias: 
<br>
<% @categories.each do ||%>
...
<br>
<% end %>

route.rb

get "search" => "search#index"

search_controller.erb

class SearchController < ApplicationController
    def index
            search_word = params[:q]
            @products         = Product.search(name_cont: search_word).result
            @articles         = Article.search(name_cont: search_word).result
            @municipalities   = Municipality.search(name_cont: search_word).result
            @enterprises      = Enterprise.search(name_cont: search_word).result
            @categories       = Category.search(name_cont: search_word).result
    end
end