1.  form_for

<%= form_for(@article) do |f| %>
  <%= f.label :title %>
  <%= f.text_field :title %>
<%end%>

In this example i supplied an object of article to the form_for method.

It will generate the following:

<form action="/articles" class="new_article" id="new_article" method="post">
    <label for="article_title">Title</label>
    <input id="article_title" name="article[title]" type="text" />

• text_field

<%= f.text_field :title %>

For text_field there must be an existing column in the database like in this case you must have a column name 'title' in the database.

It is always used with the combination of form_for.

•  radio_button

<%= f.radio_button :contact_method, 'email' %> 
<%= f.label :contact_method, 'Email', :value => 'email' %>

They are generally used for small selection list.

They are generally created as an independent object that are united together by a naming convention.

•  check_box

<%= check_box("notes", note.id, {checked: true}) %>

By default it's value is set to true which means it will be checked by default.

2. form_tag

Syntax:

<% form_tag(articles_path, :method=>'post', :multipart => true) do %>

You simply defines the path to the form_tag.

Then you define it what HTTP request to make like in this case you are making a 'post' request.

•  text_field_tag

<%= text_field_tag :email %>

text_field_tag is used if we do not want to involve the database.