How to block private messages/friend requests (from another member)
Visit the profile of the member you wish to block and click the "More" menu under the avatar, then choose block and confirm.
How to block a member's posts:
You can also block and unblock a member from any interact button under any of their posts. Go to any post, go under their avatar, choose 'more' then choose 'ignore user's posts' or 'block'.