How can I create a copy of my CiviCRM site?
There are some instructions at https://docs.civicrm.org/sysadmin/en/latest/misc/switch-servers.

The wiki page referenced in a couple similar questions is still there but getting out of date, and there's something wrong with the styling at the moment, but it's still legible: https://wiki.civicrm.org/confluence/display/CRMDOC/Moving+an+Existing+Installation+to+a+New+Server+or+Location