I can never actually remember the order and the number of parameters so here they are:

The above example means, at 5:00AM every single day, run the ~/backup.sh command.  Of course you can change the numbers to match what you intend to do.

Here is something you can paste into your crontab if you want to have a handy reference of what each parameter means:

#minute, hour, day of month, month, day of week, command

Make sure that you have the "#" at the beginning of the line which means it is a comment and that the contents won't try to be interpreted/executed, this will break your crontab entries.