Once your character and wand have been selected, you’re ready to start moving around the wizarding world. As you approach your first portal you will meet Garrick Ollivander, the owner of Olivanders wand shop in Diagon Alley. You can remind yourself about Diagon Alley here.
Ollivander will be an augmented reality character that will appear to be in real life when viewed through your phone. He will greet you and invite you into his shop in Diagon Alley (using a portkey) that will start an animation in which you will choose your wand.
Find out more about Garrick Ollivander at https://www.pottermore.com/explore-the-story/garrick-ollivander