A question about rails view code

I am new to rails. I read some examples and don't understand rails erb syntax. There is a piece of code I am not familiar:

<% form_for(@bay_info) do |f| %>   <%= f.error_messages %>

  <p>     <%= f.label :HostName %><br />     <%= f.text_field :HostName %>   </p> ...

I wander what f mean. What is its type? How can I find its definition?

thanks.

I am new to rails. I read some examples and don't understand rails erb syntax. There is a piece of code I am not familiar:

<% form_for(@bay_info) do |f| %> <%= f.error_messages %>

f is a form builder. If my memory is correct the docs for form_for
should have some details.

Fred