They have wifi turned off.
They are being blocked by Barracuda and need to authenticate.
They entered their network credentials incorrectly.
They are on the wrong wifi.
Non of the above
Go to Settings, Mail, Contacts, and Calendar, then Add Account.
Go to Photos, Select a Photo, Select Share (by email), and follow the prompts to add an email account.
Go to Mail, Contact, and Calendar, then Settings, then Add Account
None of the above.
Top left corner
Top right corner
Bottom left corner
Bottom right corner