Here are some ways it's commonly used:
* Information: "More detailed information about the project is available upon request." (The information isn't readily accessible, but you can get it if you ask for it.)
* Documents: "The full report is available upon request." (The report isn't publicly shared, but you can request a copy.)
* Services: "Free consultations are available upon request." (You don't get a consultation automatically, but you can ask for one.)
* Products: "Limited edition merchandise is available upon request." (These items aren't stocked in stores, but you can order them if you want them.)
In essence, it indicates that something is there, but you need to make a conscious effort to ask for it.