app/views/users/_form.html.erb
<div class = "col-md-8">
<%= simple_form_for @user do |f| %>
<%= f.label 'First Name'%>
<%= f.text_field :first_name, error: '', class: 'form-control' %>
<%= f.label 'Last Name'%>
<%= f.text_field :last_name, error: '', class: 'form-control' %>
<%= f.label 'Email' %>
<%= f.text_field :email, error: '', class: 'form-control'%>
<br />
<%= f.submit class: "btn btn-primary"%>
<% end %>
</div>