You can use crontab by running:
crontab -e
Then paste in your cron-specific command, such as:
0 8 * * * /usr/bin/wget http://domain.com/file.tar.gz -O /path/to/file.tar.gz
The above command will download the file file.tar.gz and store it to /path/to/file.tar.gz. You will need to create the storage directory beforehand, though. The command won't create it for you, so you could run:
mkdir -p /path/to
You can also change the file name and add a date if you need to keep previous versions.
0 8 * * * /usr/bin/wget http://domain.com/file.tar.gz -O /path/to/file_$(date +%Y%m%d_%H%M%S).tar.gz
Which would produce a file name such as file_20161014_091953.tar.gz