You can edit the cron file using the following command:
$ sudo crontab -e
You can add a new line like the following:
30 8 * * * echo "test" >> /tmp/test
In this case, a "test" line will be added in the /tmp/test file at 8:30 every day. You can check your cron tasks with:
$ sudo crontab -l
Note: for nano, F3 -> save file but not exit, then press ENTER to confirm file name to save. 