There are two examples that show.
https://www.wix.com/corvid/example/exposing-apis
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-myapi-and-myapiclient
When you say installed and you actually mean the ups shipping api npm that was added to Wix Package Manager in March of this year, then you follow the examples here and look at ups shipping own npm documents to see how to use it.
https://support.wix.com/en/article/corvid-managing-external-code-libraries-npm-with-the-package-manager
https://www.npmjs.com/package/ups-shipping-api
Please note too that it is actually not connected with UPS so you won’t get help from them.
This is an unofficial node.js package that makes interacting with the UPS api easy. Uses the UPS json endpoints.
These examples show you how to use a npm.
https://www.wix.com/corvid/forum/community-discussion/example-send-email-with-the-sendgrid-npm-interface
https://www.wix.com/corvid/forum/community-discussion/example-google-sheets-npm
You should also have a read of Wix HTTP Functions and Wix Fetch.
https://www.wix.com/corvid/reference/wix-http-functions.html
https://support.wix.com/en/article/corvid-exposing-a-site-api-with-http-functions
https://www.wix.com/corvid/reference/wix-fetch.html
https://support.wix.com/en/article/corvid-accessing-third-party-services-with-the-fetch-api
https://www.wix.com/corvid/example/exposing-apis
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-myapi-and-myapiclient