Step 1 : crontab -e
Step 2 : Select your prefered editor for the file.
Steo 3 : Add the command that you want to execute from cron and save that file.
Example : 1 0 * * 0 rm /home/jones/*.log > /dev/null 2>&1
Step 4 : check if cron is activate using command
crontab -l
# As others have pointed out, the first thing is to make sure you're
# using an editor you like.
# We're all admins here, so we all like vi (ducks, runs).
export VISUAL=vi
crontab -e
# (do some edits, finishing with ESCAPE)
:wq # ENTER
crontab -e # open user crontab in edit mode
i # for insert. Make your changes
:wq! # quit and save
crontab -l # open user crontab in read mode
(crontab -l 2>/dev/null; echo "*/5 * * * * /path/to/job -with args") | crontab -