You would use form_for for a specific model,
<% form_for @person do |f| %> # you can use f here
First name: <%= f.text_field :first_name %>
Last name : <%= f.text_field :last_name %>
<% end %>
Form_tag create basic form,
<%= form_tag '/person' do -%>
<%= text_field_tag "person", "first_name" %>
<% end -%>
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