How to set up a redirect in htaccess?

Question

htaccess

Good afternoon.
I have a landing page that needs to be loaded when you first enter the site. Further, the user can already go through the menu to other sections.
How can I make it so that when accessing www.site.ru , there is a redirect to www.site.ru/main.php and then the user himself would walk?
I know how to make a redirect, it's just that on subsequent calls to Index.php you will be redirected to main.php