How To Send
After made your own form, send it.
$player->sendForm($form);
Lets have a full example
public function testForm($player) {
$form = new CustomForm(function (Player $player, $data) {
var_dump($data);
});
$form->setTitle("Form Title");
$form->addLabel("Text");
$form->addToggle("Toggle");
$form->addSlider("Slider", 1, 100);
$form->addStepSlider("Step Slider", ["5", "10", "15"]);
$form->addDropdown("Dropdown", ["1", "2", "3"]);
$form->addInput("Input", "Ghost Text", "Text");
$player->sendForm($form);
And thats it you just send your first form.