You can catalogue websites, documents and other online content in the same way you catalogue a book.
Each catalogue record for an online resource includes a web address or URL for the item. Through the search screens of your ILS, students can simply link directly from your catalogue to the resource they've found.
Linking to curated content
If you've curated content using a curation tool, you can provide access to this through your library catalogue. Create a record as you would for a website and include the link to your curated content.
If you use SCIS, they provide catalogue records for websites that you can download.
Keeping online resources up-to-date
It's a good idea to check the links in your catalogue from time to time by running a link checker which identifies links that are no longer working.
Check with your ILS vendor to see if your ILS comes with this functionality.