crontab -e will create a file, but you don't need to know about that and should never edit it by hand.
man crontab shows you the various options, most important ones being:
crontab -e edit
crontab -l list
Notice that your environment as a cron job is quite different from the one you are used to in an interactive shell. Easiest to inspect this is to set a cron job as follows:
* * * * * set > /tmp/environment.log
# | | | \day of week 0-7 (0 or 7 is Sun, or use names)
# | | \--month 1-12 (or names, see below)
# | \----day of month 1-31
# \------hour 0-23
For the syntax of the crontab itself check
man 5 crontab.
Then wait for a minute and remove the cronjob again, because otherwise this nonsense job will run every minute.
Then check the difference between the interactive shell (just type
set) and the cronjob (just type
cat /tmp/environment). Especially
SHELL may surprise you.