How do i make my wordpress website private?

You can simply check if the user has an specific role, and redirect them to homepage if they try to access the admin panel.

function redirect_to_front(){
    // Check if we are on the admin panel, and the user is not an admin
    if( is_admin() && !current_user_can( 'administrator' ) ){
        // Redirect them back to front
        wp_safe_redirect( site_url() );
        exit();
    }
}
add_action('init', 'redirect_to_front');

This is just an example. You should alter the code, and change the capabilities to fit your purpose. The current_user_can() function accepts both capability and roles.