If you do one thing, and then something else right afterward, you do it next. If you hear a game show host scream, "Come on down, you’re the next contestant," then you better get to the stage!
If you're standing in line for ice cream right behind the person ordering a large hot fudge sundae, you're next. Things happen next in terms of time when they occur immediately after: "First we'll eat the appetizer, and next we'll eat the entree." The Old English source is niehsta, "nearest or closest." Your "next door neighbor" lives in the house or apartment right beside yours.