To connect your account with Facebook, you first need to verify your account. Your account can be verified by going to 'Edit Profile', then scroll down to the 'Manage Login Email' section, where you can verify your account.
Click 'Request Verification Link', and an email with the verification link will be sent. Open the link in the email to verify your account.
Now you're ready to link your account to Facebook. Keep in mind your account can only be linked if your Facebook and PosterMyWall login emails are identical. Log out, go to the main page, and click the 'Log in' button on the top right of your screen. On the login page, click the Facebook option. This will link your PosterMyWall account with your Facebook account.