Following other users
When you look at the profile of another user, you can see a green 'Follow' button at the top (figure 1).

figure 1: the follow button

Click this button if you want to follow the user. You will see this user appear in the 'Following' list on your profile, making it easy for you to access this user's profile. If this users follows you back, he/sho will also appear on your 'Buddies' list.

The user you follow will be able to send you direct messages. This user will also appear in the 'Following' list on the leaderboard.

To unfollow a user, go to their profile and click on the orange 'Unfollow' button at the top of their profile (figure 2). The user will now be removed from your 'Following' and 'Buddies' lists and will not be able to send you new messages.

figure 2: the unfollow button