if you have a form like this
<form action="/users/create" class="new_user" id="new_user" method="post">
<label for="user_email">Email<br />
<input id="user_email" name="user[email]" size="30" type="email" value="" /></div>
<input name="commit" type="submit" value="Sign in" />
</form>
In your controller 'create' action
def create
email = params[:user][:email]
#your code
end
a more simple example would be
<input id="search" name="search" size="30" value="" />
you could get this from the corresponding controller action as
search = params[:search]
If you see the log, you could see how these parameters are passing (Ex: log/development.log)
here is a sample
Processing by Devise::SessionsController#new as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"SOTgZaxt3oGsn0UQrK8Bz9dQgDjACGOIoJoxGsfCM7Q=", "user"=>{"email"=>"", "password"=>"[FILTERED]", "remember_me"=>"0"}, "commit"=>"Sign in"}
HTH