Depends on how you want to do the back up.
If you mean instantly writing to the backup external drive, sort of like a RAID configuration, I can't help you.
If you mean a regularly scheduled back, there are options available that should work great for you.
You can use Microsoft's built-in backup to perform backups, or you can use a 3rd party solution.
I've never really liked Microsoft's backup programs, so I use a free program called Cobian Backup, http://www.educ.umu.se/~cobian/cobianbackup.htm
It is very simple to use. You can set up any schedule you want: daily, weekly, monthly, etc. You can do full backups of everything on your laptop, or only files that have changed or are new since your last back up.
It provides you with the option to use shadow copy, which means it canback up files currently in use (typically those are system files).
It can compress the files to save space and can also encrypt the back ups for security if desired.
I use it on 8 workstations to back up all new and changed files nightly, and to do a full system backup every 30 days and it works flawlessly for me.