A zipped file of the theme looks like this theme-name-x.x.x.zip. This is the file that you should upload as a theme install pack via the WordPress admin panel or another way.
An archive file that contains additional material of the theme (this can be documentation, pictures, etc.) so looks like this theme-name-docs.zip. It doesn’t need to be uploaded. You can unzip it and use the files you find there.
Installation via the WP Admin
To upload through your WP Dashboard, select Appearance and then Themes. Next, select the Install Themes tab at the top of the page and then select the Upload link, right above the search field. Choose your file and select Install Now. Once the theme is fully uploaded and installed, click Activate to activate the WordPress theme.
When uploading your theme with the installer, please ensure you are uploading the theme .zip file, not the entire package you downloaded. In this case, you will be uploading theme-name-x.x.x.zip where x.x.x is the version number.
Installation via FTP
Alternatively, you can also install the theme directly to your server with a FTP client (e.g. Filezilla). Just drop the unzipped theme folder into your …/wp-content/themes/ folder.
Now you can see the uploaded theme in your WordPress admin panel under Appearance > Themes > Available Themes. From there you can activate the theme.