Tentatively means hesitantly, like how you go about a delicate or dangerous situation. It also refers to uncertainty, like when you tentatively make plans to go to a party, even though you don't have a ride yet.
It makes sense that the English adverb tentatively stems from the Latin tentare “to feel, try,” because to do something tentatively means to test it out. Think of how you slowly wade into a freezing cold pool. You’re moving tentatively, because you know it’s going to be a shock and you want to give your body time to adjust. The opposite of tentatively is certainly, a word that indicates no hesitation.