A “Miscellaneous Objective” is a small quest that isn’t quite big enough to be a quest and so is classed as an MO. These can involve visiting a museum in Dawnstar (which triggers a mission), visiting someone, following up on a lead, seeking out a source of power, clearing out a bandit camp and so on.
To see what you have activated in the MO menu and what you can do (you can even tag them on the map as well), then hit the start menu and on the quest tab, scroll down to the bottom of the incomplete quests section and then move right and see what you’ve got to do.
If you want to add stuff onto here then try talking to barmen about rumours and generally speak to people galore, probing for tidbits of information and so on. You’ll find all the courier "quests" and barmen bandit clear outs fall under this heading, so if you’re wanting to do some, you know where to head first.