Before cloning a site, you need to know how you can backup a WordPress site.
So, You know the Most important thing in cloning requires Database. You can simply export the MySQL file and change the URL to new site URL and save it.
Unzip the files from old site to new site URL.
Upload it to new WordPress Install and then unzip it. Import the MySQL and you are ready to go.
Clone WordPress site using Plugin.
Backup plugins like UpdraftPlus premium provide the facility to clone and migrate sites in simple clicks.