Double switching is like changing your clothes twice. Let's say you have two sets of clothes: one for playing outside and one for going to a party. When you're playing outside in your causal clothes and you get invited to a party, you have to change into your party clothes. But, if you suddenly realize you left something outside in your casual clothes, you have to change back into them again before returning to the party. That's basically what double switching is - changing your clothes twice back and forth.
Now, in a game of baseball, double switching is when a team changes two players at the same time during a game. Instead of just one player replacing another player, two players are changed. This happens when a team wants to change their fielding positions as well as their batting order. Think of it like swapping two clothes hangers in your closet - you're moving the position of two items at the same time. This is typically done by the manager of the team to strategically improve their performance during the game.