The memories option will be located on Snapchat Marketing Services on the opening screen where you take a photo or video. It is a little circle under the camera button. In case your screen is blank in the memory section then you can head to your camera roll where you need to select the videos and photos that you want included in your memories. On clicking the check mark in the upper right hand corner you can scroll through the saved pictures and video and touch it to compile them. After choosing the videos and the pictures that you would like to put together to form a story, you would then press the down at the bottom icon, a circle with a plus sign.