Once you connect your frame to WiFi, the app will ask you to grant it permission to access your photos. Make sure you click "Allow" or your frame won't work.
To manually choose individual photos for your frame, open the Aura App and click into Photos, Collections or Albums. Select the photos for your Aura Frame by checking the small circle on the bottom right of each photo (a green check will mark the selected photos). All the photos you have checked will be added to your Selected photos in the app.
You may also choose to select photos using Smart Select which is available for Albums and Collections. Smart Select will filter your photos, displaying the best ones on your frame. If you have an Album or Collection set to Smart Select, any new photos you add to that album or photos you take of that person will automatically be uploaded to your frame.