Okay. Better question then. Why doesn't the standard tutorial OR the 'Learning scenario' touch on that topic? Make your courtiers happy by marrying them off, but that's not an option for vassals (and no in-game feedback about why an action failed or works differently when applied to a character already working for you).
Having 2 different interfaces (the R-Click and the Rings) for the same function, but using different restrictions / rules is a potential issue, especially from a new player's perspective. I've been in the game for only 8 or 9 hours total, in a couple of different countries; my current knowledge is limited, but I'm exploring. My initial observation is that the interface is dreadful.
Back to the initial issue, Ragnvald had the Rings interface exactly once -- the very first time I played as Murchad when Ragnvald first got the 'Get Married' ambition, On that instance, the Rings tried to marry someone in my court to someone in his court (apparently). I believe it occurred the first time I tried the 'Learning Scenario', but I don't have the specific details on that. I haven't had time to explore this further with other countries (maybe only an issue on the first time playing a country with this specific configuration?) I haven't been able to get the Rings interface to reappear, so I considered it a possible 'initial use' bug.
I'm still trying to work with Steam to see what DLC / expansions I purchased -- I thought the package I bought included Charlemagne and The Old Gods (I knew about those expansions and wanted both), but Steam doesn't show any DLC for my account, even to the point of not having a DLC tab on my CKII game properties interface. Hopefully, that will teach me to buy something and let it sit around a month before checking it out (especially with Steam). I suspected (and still do suspect) that this issue was related to not having some specific expansion DLC. Thought I'd iron out what exactly I'm supposed to have, get it installed and updated, then worry about reporting issues or asking questions.
I was replying that this wasn't an isolated incident, merely supporting
@Gungar's initial post with another observation along the same line (recent purchase and marriage issues). It may be entirely a learning issue. It appears to be something else, though, especially with another person experiencing similar problems. Maybe there is a problem with CKII w/o DLCs, and maybe Gungar is having a similar issue. I appreciate that I may not know the game well, but the circumstances of my installation details and Gungar's unstated installation details might help him or the developers who might trying to chase this problem. I did not expect any long time player, who probably has several expansions to the game to experience the same issue, but I do appreciate the help, Dracko81. I did learn something by Gungar's issue -- I won't confuse the entirely-too-similar Betrothal and Marriage interfaces in the future.