Someone who's confrontational isn't shy about arguing forcefully — in fact, it's the way they often interact with other people. When guests on a TV talk show start yelling at each other, you can describe it as confrontational.
When one person confronts another, they argue face-to-face — this interaction is confrontational. The Medieval Latin source of these words is confrontare, which simply means "adjoin," or "be next to," from the Latin roots com-, "together," and frontem, "forehead." So you could think of a confrontational situation as one in which two people are disagreeing while so close that their foreheads nearly touch.