My microsoft word and excel are not working after I installed Mac OS Catalina

This issue is on MacOS Catalina now does not support 32 bit apps and MS Office is 32 bit software. It was stopping support a few years back and will not be updated.

You will have to buy a latest version of MS Office or you can use alternative software like G Suite by Google and much more. The same problem with me when i am update my company Profile App of LogoDesign, i have to reinstall the 64 bit MS Office for its overview and reporting sheets but now its all working perfectly. You can get it from here, https://products.office.com/en-us/compare-all-microsoft-office-products

If you have Office 2016 32 bit you can get a free upgrade to Office 2016 64 bit. Otherwise you need to purchase a 64 bit version.

Microsoft Office 2016 (updated), Office 2019, and Office 365 all work with Catalina. If you have an older version of Office you need to upgrade Office to one of these 64 bit versions.

Depends on what version you have. Go to the Microsoft site for the details.

Current Purchase Microsoft Office Options