Multiple exposure is a technique that combines two images into one by overlaying them. It allows effects like ghostly or mirrored images. While some cameras provide a multiple exposure function, photo editing software like Photoshop provides more control by allowing images from different times to be combined. Light writing involves long exposure photography where lights are used to create effects and objects by moving them during the exposure. A tripod is important to avoid camera shake, and different light sources can be used along with settings like a high aperture number and low ISO to reduce noise for long exposures.