When you do something humorously, you're being comical, or trying to get people to laugh. If you're auditioning for a role in a comedy, be sure to deliver your lines humorously.
If you do a lot of things humorously, you probably also find yourself saying, "Just kidding!" all the time. This adverb implies playfulness and a joking quality, so you might speak humorously about a serious subject to lighten the mood, or write humorously in order to make your friends giggle helplessly when they read your story. The word comes from humor, which today means "the quality of being amusing," but originally meant "bodily fluid."