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.
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?