Both form_for and form-tag are Rails helper methods. Whenever we want to build a form containing various elements like text-fields,text-areas,labels etc, we simply need a form builder object.

form_for rails helper method just do that, it provides a form builder object to help creating a form.

A typical example is given below;

<%= form_for @event , url: user_events_path(current_user.id) do |f| %>
<p>
	<%= f.label :description %><br>
	<%= f.text_area :description %>
</p>
<p>
	<%= f.label :venue %><br>
	<%= f.text_field :venue %>
</p>
<p>
	<%= f.label :date %><br>
	<%= f.date_field :date %>
</p>

<%= f.submit %>

here, first argument it receives is an object of a model class. Second argument is a hash having key name url and value as a named route. The  block variable f is just that form builder object I was talking about, it simply creates three labels and their corresponding value holders.

When we submit the form it gets submitted to the given action. The params hash now will have a key named event and it's value will be an another hash having description,venue and date as key names and their corresponding values as their values.

The config/routes file is having a nested resource

 resources :users do
    resources :events 
    
  end

and rake routes gives us

  user_events GET    /users/:user_id/events(.:format)   events#index
              POST   /users/:user_id/events(.:format)   events#create
new_user_event GET    /users/:user_id/events/new(.:format)     events#new
edit_user_event GET    /users/:user_id/events/:id/edit(.:format) events#edit
    user_event GET    /users/:user_id/events/:id(.:format)       events#show
               PATCH  /users/:user_id/events/:id(.:format)       events#update
               PUT    /users/:user_id/events/:id(.:format)       events#update
               DELETE /users/:user_id/events/:id(.:format)       events#destroy

thanks.