I want to add a new question to the default page

hi
I am Japanese. This sentence is written using Google Translate.
I am sorry if there was an obscure part.
I would like to add a new question to the default page.
I saw the following page, but I do not understand it deeply.
And there are things I wonder a couple of questions.
https://anspress.io/resources/faq/anspress-form-and-validation-api/
1. Where do I install custom-form.php? Is it in “anspress-master” folder?
2.

anspress () -> get_form ('sample_form') -> generate ();

in which file do you write?
3.override-ask-form.php, sanitize-validate-field.php, save-custom-form.php Three of these are not sure where to install.
I want to add a new question to the default page even if only one thing is done, but I do not understand easily because I translate sentences and read it.
If I do not deepen understanding a little, is it possible to achieve my purpose?