gistfile1.php

<?php

class MyForm1 extends Form {
    public function __contruct($controller, $name) {
        $fields = new FieldList([
        	new TextField('FirstName', _t('MyForm1.FirstName', 'FirstName')),
        	new TextField('LastName', _t('MyForm1.LastName', 'LastName')),
        ]);
        $actions = new FieldList([
        	new FormAction('SendMyForm1', _t('MyForm1.SendMyForm1', 'save')), 
        ]);
        $validator = new RequiredFields([
            'FirstName',
        	'LastName',
        ]);
    	parent::__construct($controller, $name, $fields, $actions, $validator);
    }
    public function SendMyForm1($data) {
        // do something with the data
    	Debug::log(print_r($data,1));
        // redirect to the next step
        $c = $this->Controller();
        return $c->redirect($c->Link('MyForm2'));
    }
}

class MyPage extends Page {}
class MyPage_Controller extends Page_Controller {
	private static $allowed_actions = [
        'Step1',
        'Step2',
        'Step3',
    	'MyForm1',
        'MyForm2',
        'MyForm3',
    ];
    
    public function index() {
        // uses template MyPage.ss and falls back to Page.ss
    	return $this;
    }
    
    public function step1() {
        // uses template MyPage_step1.ss and falls back to MyPage.ss, Page.ss
    	return $this;
    }
    public function step2() {
        // uses template MyPage_step2.ss and falls back to MyPage.ss, Page.ss
        // and puts MyForm2 into the template variable $Form, so you could also use MyPage.ss for all steps
    	return $this->customise([
        	'Form' => $this->MyForm2(),
        ]);
    }
    
    public function MyForm1() { return new MyForm1($this, __FUNCTION__); }
    public function MyForm2() { return new MyForm2($this, __FUNCTION__); }
    public function MyForm3() { return new MyForm3($this, __FUNCTION__); }
}