Hi Vilma,
I don’t understand what exactly you’re trying to achieve. The registration form is not made to be displayed on the homepage.
An alternative that might suits your need might be to display the login form in a popup by going to Customize > Appearance > Login and selecting “Display login and register buttons in the navbar”. Then, select “Display login form in a modal”.
In case you wanna force the users to login, we recommend My Private Website to make you entire website private. Simply install and activate this plugin, and then go to the plugin settings page (Settings > Private Site) in order to adjust options according to your needs.
If you need more help, this tutorial seems to explain every steps in great details: How to Make Your WordPress Blog Completely Private.
Hope this will help you.
Best regards,