Actually, making a false memory is pretty easy. Loftus describes a father convincing his daughter she'd gotten lost in a mall when she was five years old. At first, the daughter denied any memory of the event, but as the father provided more fake details-"Don't you remember that I told you we would meet at the Tug Boat"-the daughter began to "remember" and even provide details of her own. Eventually when her father said "I was so scared," she responded "Not as scared as I was!"
Loftus also showed subjects a painting of a country scene and then asked them to remember it: the trees, the waving grain, the barn. Only, there was no barn in the image. Even though subjects knew there was no barn when they looked at the painting, those in whose heads the idea was planted recalled a barn when asked about it a couple weeks later.