The United Nations produces a massive amount of documentation, much of which is now available on the web. If it's a document produced in the last ten years and you have the UN document number, it's usually pretty easy to find a PDF. However, the older the document is, the more likely it is you'll have to send the student to the microform collection at Van Pelt, or to a source in print instead. Also, be aware that not every UN document is publically released, so dead ends are always a possibility.
For exhaustive tips on documents research, see the Dag Hammarskjold Library's outstanding guide (with videos!). I have also found the librarians fantastically helpful, as they will often scan and send you documents that are not yet in the ODS, as long as you can afford to wait a few days.
UN documents are always labeled with a long, convoluted unique symbol involving abbreviations and forward slashes, e.g. A/RES/49/10. Although it can be helpful to know what all those components mean, it's not strictly necessary. Provided the patron has one, go through the following steps to find the document:
1. Enter the number into the "Search by Symbol" box on the UN Documents Centre page. A significant amount of the time, the PDF will pop right up, although you may first have to choose which language you want it in if there are multiple versions.
2. If you get a "document not found" error, try reverting to the old ODS search page. Some documents just haven't been moved into the new system yet.
3. If it's not in either version of the ODS, try running a Google search using the document number.
4. If that fails, go to the website of whichever UN agency or body issued the document and look around their documents or publications pages. Google hasn't managed to effectively crawl all of them, and the UN website is also constantly moving things around, leading to broken links.
5. If you're still not finding the document, refer the patron to me and I'll help them navigate hard copies or confirm that the document's not available.
If they don't have a document number but do have at least some information about the document (title, date, issuing body), try the following to locate a document number and then go through the steps above:
1.Consult one of the UN Library's documents indexes, UNBISnet and/or UN-I-QUE . The former has a more comprehensive search interface and, especially for newer documents, will provide links directly to the PDFs in the ODS. However, since not all documents have made it into UNBISnet, you may need to rever to UN-I-QUE for basic title and number information.
2. If it doesn't come up in one of those indexes, try the commercial AccessUN index to the READEX microform series. Some records will offer full text (albeit in HTML, which will be useless for source hunters), but most will have only a description and title/document number information instead.
If the above fails, refer the patron to me and I'll use some additional, less user-friendly tools to try to find the document.