What is the difference between a citalopram and a Xanax?

Citalopram is an antidepressant of the SSRI class. It's used to treat depressive disorders and anxiety/panic disorders. It's used to treat these conditions on a long term basis.
Xanax is a benzodiazepine, a controlled substance, that treats anxiety disorders, panic disorders, and anxiety caused by depression on a short term basis. It's a sedative/tranquilizer.
I hope this helps. If you have other questions or concerns you can always post them.
This tool may also help:
https://www.drugs.com/compare/xanax-vs-citalopram