To follow another user on Clash, just tap on their profile pic/name to enter that user's profile page. Once on the users profile just tap the "follow" tab to follow that user.

It's that easy!

If you no longer wish to follow a particular user, simply return to their profile page and tap on the horizontal ellipsis (3 dots) found in the top right of the screen. You will now see a few options displayed, tap "Unfollow" to remove that user from your followers list.