How to redirect a website using .htaccess?

Redirect website http://mydomain.com to http://www.mynewdomain.com

RewriteEngine on
RewriteCond %{HTTP_HOST} ^mydomain\.com$
RewriteRule ^(.*)$ http://www.mynewdomain.com [R=301,L]

Redirect website mydomain.com with and without www requests to http://www.mynewdomain.com

RewriteEngine on
RewriteCond %{HTTP_HOST} ^www\.mydomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^mydomain\.com$
RewriteRule ^(.*)$ http://www.mynewdomain.com [R=301,L]

Redirect requests from http://mydomain.com to http://mydomain.com/subdirectory i.e. redirecting requests from main domain to a sub-directory.

RewriteEngine on
RewriteCond %{HTTP_HOST} ^www\.mydomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^mydomain\.com$
RewriteRule ^(.*)$ http://www.mydomain.com/subdirectory/ [R=301,L]

Redirect all http (80) requests of a domain to https (443) i.e. redirecting requests from non-secure port to a secure port.

RewriteEngine On
RewriteCond %{SERVER_PORT}      !443
RewriteRule ^(.*)$ https://mydomain.com/$1 [R,L]