To block someone, just open their chat or profile and tap on the three dots in the upper right corner, followed by selecting the option to block them. Be sure of the action, and they will no longer be able to contact or see your content.
To block someone on Snapchat, open the app, go to your Chat or Friends list, tap and hold the person's name, then tap "Manage Friendship" and select "Block." Confirm when prompted. This will prevent them from contacting you or seeing your content.
