Goto /d8codebase/sites/sites.php file.
Add below array
$sites = array(
| ||
|
Then create site1, site2 folders inside /d8codebase/sites/ folder
Like in D7, Inside site1 and site2 folders create separate settings.php and add the database and other configurations specific the site.
Add site1.com and site2.com in vhosts file.