I defined the form in my page controller.

function SignUpForm() {
//$field = $this->dataFieldByName('Title');

// Create fields
$fields = new FieldSet(
//new TextField($name = "Seminar Name", $title = "Seminar Name", $value = Title),
new TextField($name = "name", $title = "Name", $value = ""),
new TextField($name = "company_name", $title = "Company Name"),
new TextField($name = "phone_number", $title = "Phone Number"),
new TextField($name = "email", $title = "Email"),
new HiddenField ($name = "Seminar_Name", $value = "???????")
);

// Create actions
$actions = new FieldSet(
new FormAction('doSignUp', 'Sing Up')
);

return new Form($this, 'SignUpForm', $fields, $actions);
}

My hidden field is supposed to have the title of the page as value.

I tried to do like this:
$field = $this->dataFieldByName('Title');
new HiddenField ($name = "Seminar_Name", $field->Title)

but it doesn't work.

Also some fields are supposed to be required. How would I do that?

thanks

You want the page title? Then you would use $this->Title and the value is also the 3rd parameter I believe so you need to have a title

new HiddenField("Seminar_Name", "Seminar_Name", $this->Title);

For required fields see http://doc.silverstripe.org/doku.php?id=tutorial:3-forms#form_validation

Thank you