You can put individual character warnings by going on the character's profile and clicking "Manage Character" > "Warnings"
Content warnings are used to warn viewers about any triggering and/ or sensitive content. In other words, if your character features any kind of content that most people might find distressing/ upsetting, then it should have a warning. I have a profile warning snippet here with already listed sensitive subjects that would normally warrant a warning, but you should use your own judgment. How I usually determine if something needs a warning is by asking myself "would I be comfortable talking about these subjects with a young child and would they be comfortable listening to me talk about it?" If yes, I would put a warning just in case; if not, then it's probably safe to just leave it as is.