To follow your friends, open the mobile app for smartphone or tablet and navigate to Activity (from the tab menu at the bottom). From Activity, tap the icon at the top right that indicates a person.
In the next window, you can connect your address book and/or your Facebook account if you haven't already. Tap on either circle to link your accounts and find your friends who are using Blinkist. You'll also see an option to invite people to join you on Blinkist.
You will be able to see what your friends are reading and highlighting in the Activity Feed (as long as they've enabled this in their settings. It is possible to disable this sharing in your own settings, too). It is not possible to browse your friends' profile or library yet, but it may be available down the line.