Is cron command supposed to work like this? I've set up cron to run a script hourly but when I reboot cron does not work. Does this mean that I should run cron whenever I boot into my Mac? The cron command which I use cron 5 * * * * path/to/script.sh. Is there any problem with cron or I this kind of behaviour expected?
You don't need to call cron directly. Any commands you want to run need to be added to the crontab of the user they should run as. You can edit your crontab by running

crontab -e


or, if you are an admin user and want to edit the crontab of another user,

crontab -u USERNAME -e


PS: Run man 5 crontab for details about the format of the file, what kind of special commands you can use, and some samples. 5 * * * * /path/to/script seems to be ok though.