Children often express their emotions more openly and honestly than adults do. As grown-ups, we learn to filter what we're really thinking in order to avoid hurting other peoples' feelings. Children haven't learned that skill yet. If they think you're not making any sense, they'll let you know about it - often with a big 'I have no idea what's going on right now' shrug, as Good Luck Charlie does in this famous meme. It's commonly used to mock people on Twitter post nonsensical arguments.
In the case of this meme, the name has been taken from the television show that featured the footage; 'Good Luck Charlie' was once a fixture on the Disney Channel. 'Charlie' is actually Mia Talerico, who's still only ten years old, and remains active in the world of acting. She could probably still pull off that completely dismissive shrug if she wanted to, too.