ROR is a unique ID for institutions--like ISSN or DOI, but for research organizations.
Or, in the words of their website, "ROR is the Research Organization Registry, a community-led project to develop an open, sustainable, usable, and unique identifier for every research organization in the world.
Unsub uses your institution's ROR in several ways, but the most important is to help improve our accuracy in tracking authorship and citations from faculty at your institution.
When you sign up for an Unsub account, we load your ROR in for you, so there's nothing you need to do about ROR. In the future you'll be able to upload other RORs, in case your institution has more than one of them (sometimes institutions have one main ROR and another one for their medical school, for example).