_form_i_want.html.erb

<p>
            <%= form_for([@photo, @tag]) do |f| %>
                <div class="field">
                    <%= f.label :key %>
                    <%= f.text_field :key %>
                </div>
                <div class="field">
                    <%= f.label :value %>
                    <%= f.text_field :value %>
                </div>
                <%= f.submit "Tag Photo", class: "button success" %>
            <% end %>
</p>

home_controller.rb

class HomeController < ApplicationController
  def index
  	@user = current_user
  	@photos = Photo.all
  end
end

index.html.erb

<h1>All Photos</h1>

<div class="row">
 <%  @photos.each do |photo| %>
 	<div class "row">
		<h2>  <%= photo.title %> </h2>
		<% if user_signed_in? && photo.user_id == current_user.id %>
  			<%= link_to image_tag(photo.image.url(:thumb)), photo_path(photo) %>
 ////////////////////I need the form here?????????????????????????????????????
    		<%= link_to 'Destroy', photo, method: :delete, data: { confirm: 'Are you sure?' }, :class => "button alert" %>
    	<% else %>
    		<%= image_tag(photo.image.url(:thumb)) %>
		<% end %>
	</div>
<% end %> 
</div>

routes.rb

Rails.application.routes.draw do
  get "tag/create"
  get 'home/index'
  root :to => 'home#index'
  resources :photos do
    resources :tags, only: [:create, :destroy]
  end

  devise_for :users

tags_controller.rb

class TagsController < ApplicationController
	before_action :set_photo, only: [:create]

  def create
  	@tag = @photo.tags.build(tag_params)
  	if @tag.save
  		flash[:success] = "Photo Tagged"
  		redirect_to @photo
  	end
  end

private
	def set_photo
		@photo = current_user.photos.find_by( id: params [:photo_id])
		redirect_to root_url if @photo.nil?
	end

	def tag_params
		params.require(:tag).permit(:id, :key, :value)
	end
end