Until now the totara sync cron task wasn't included in the main cron - so you had to manually set up another cron job to call it.

We actually have a patch in review to fix that (so the main cron runs totara_sync too) which should be in the next release.

In the mean time you should be able to manually run it with:

php -f /path/to/code/admin/tool/totara_sync/run_cron.php

It's worth running it this way the first time anyway just so you see any errors in case it doesn't work.