Upload Zipped Wordpress Files to Lightsail

The contents you have in a zip file are most likely the entire WP site and would not be what Lightsail is looking for. The .xlm file is just contents. My suggestion is you use another cheap hosting service with traditional cPanel services, reconstitute your site, then export the .xml that you can then use to import into Lightsail. The underlying files used in Lightsail will have different permissions and require a bit more work to gain FTP access for you to use the zip file as is.

Since you are a newbie, the path of least resistance would be to get your file into the .xlm that all WP sites use to import content.

One other option, if you are looking to replicate your site completely, would be to use something like Updraft, take a backup of your reconstituted site, then take a backup of the site, storing it in a cloud provider like Google or Dropbox, then just install Updraft in your Lightsail instance and restore the backup.

Hope this helps, the steps for accomplishing this should be easier to find then trying to fiddle with file placement in Lightsail...it is finicky in my experience, so be sure to take a snapshot of the instance before you make any changes. Hope this helps!