On iOS, you can search for and add friends in the app by tapping the "More" icon in the lower right corner and selecting "Friends" from the app menu. On Android, tap the "Menu" icon in the upper left corner, then select "Friends."
On the Friends page, tap "Find" in the upper right-hand corner (iOS), or the + icon (Android). You can search for friends by name, email, Facebook, Twitter, and your phone's address book. Once you locate the correct profile, tap "Add" (iOS) or + icon (Android) to send a friend request. Note that your request must be approved by your newly added friend in order for this person to appear on your friends list.
To remove friends from your friend's list, for iOS user's, simply drag your finger from right to left on your friend's name then tap "Delete". For Android user's, long press on your friend's name and then tap "Delete".
Add and Delete Friends from Website
You can find and add friends here. To delete a friend from the site you will need to access your friends list. This link should take you directly to your friend list. From here select the unfriend option next to the user you wish to delete.