Assuming your website is loading from domain.tld, you have extracted the archive into the following location, correct?
/var/www/html/
Then from there, you are navigating to domain.tld, is that right?
Did you leave all of the files in the grav-admin directory? If so, you need to navigate to domain.tld/grav-admin or domain/tld/grav-admin/admin. If you have not, I would suggest moving the files from the grav-admin subdirectory to /var/www/html/ and then navigate to domain.tld/admin.
I would also recommend downloading Grav 1.3.10 instead of 1.3.9. The latest package download is still downloading 1.3.9, which had an issue with the admin interface from the following link.
https://getgrav.org/download/core/grav-admin/1.3.10
The white page suggests you are hitting a working web service but that the index.html (or index.some_other_extension) is empty or does not load any element or CSS. Normally you would receive a 403 error if it were not reading anything.
Do you have access to the install's subdirectory?