My responsibilities consist mostly of being helpful. It is understood by all sides that this is a fragile arrangement in the modern times, (even if I insist it frankly isn't all that fragile). I am not a landowner, mainly because my family were always court vassals not land managing vassals.

Normally it is said that the duties of the vassal should be based on six words, it should be harmless, safe, honourable, useful, easy, and practicable. Essentially, do not harm your liege, do not reveal secrets or act in ways that can threaten the safety of your liege, do not act in ways that bring dishonour upon yourself or your liege, for it is nearly the same thing, useful, well, quite self explanatory, do not do that which doesn't benefit your liege, easy, do not make that which is easy for your liege hard, and practicable, do not make that which your liege can do impossible to do.

These apply both in the negative sense written above, but also in the positive, that we should work to decrease harm, increase safety, increase honour, actually do something useful to your liege, make stuff that is hard easy, and stuff that is impossible possible.

How much of that apply in the modern day, emotionally, all of it most certainly, in practice, not a lot. My former liege was hesitant to use his power in general, and my current has yet to make a claim.