Let's pretend you, user37340, I, Turtleweezard, and four of our friends are going to play a game. We all sit on the floor in a line, with me at one end and you at the other. Now, everyone except you is given a ball. The only goal of this game is to have one ball. I, being the instigator that I am, decide to shove the person to my left. This starts a chain reaction - everyone jostles the person to their left, and eventually the person directly before you jostles you. You use this chance to grab their ball. This starts another reaction - the person to your right now has no ball, so they reach over to their right and steal that neighbor's ball. (they can't take it from you, no take-backs.) This keeps happening until I'm the only one without a ball.You could say the no-ball person is moving. But in reality, no people are moving at all; we're all sitting on the floor in the same order. The balls are moving, and therefore the lack of a ball is moving also, in the opposite direction.
Now replace the people in this situation with positive ions and make the balls electrons. Even though electrons are what actually move when a current flows, we could also track the 'gaps' - the lone positive ions without electrons.