A New Site created with a consumer account will have a URL like 'https://sites.google.com/view/sitename' and if created with a gSuite account it will be like 'https://sites.google.com/domainname/sitename'
To find your site go to sites.google.com/new while signed in with the correct account and you should see your site(s) listed. If you want to create a new site, click the red + icon on that page or on the create button at the upper-left. You can also create a new site in Google Drive. Click New, select More and then Google Sites.
You can also find your site by going to drive.google.com. If you don't see your site(s) enter 'type:site' in the search box.
If your site has been inadvertently deleted go to drive.google.com and open the trash folder. If your site is there, right-click on it and select Restore. Or use this search: 'type:site is:trashed'. More instructions from Steegle.
When you find your site you will be in edit mode. To see the published site URL you must first publish the site. You will then have a button appear that links to the published site. You can also see this link by clicking the down arrow next to the Publish button.
If you want to reuse a deleted site right-click on the file in the trash folder and select Delete forever. A site name can only be reused by the same account that originally created it.