Once you have added a profile on you account page, it will show up in the app. Click on "Profile" in the lower right corner and then on "Switch Profile". Choose the profile that you want to listen or read from.
You can also switch between profiles by clicking on your profile name under your book lists in the "Home" section.
If you are missing a profile, please check that you have the newest app version installed and restart your app so it can synchronize with your account.