HTTP stands for "Hyper Text Transfer Protocol" and is used for transferring readable documents across the internet. This matches the action "You visit a website"
POP3 stands for "Post Office Protocol 3" and is used for reading e-mail. This matches to the action "You check email in your inbox"
SMTP stands for "Simple Mail Transfer Protocol", and is used for sending email. This matches the action "You send an email to a friend".
FTP stands for "File Transfer Protocol", and is used for transferring files to and from other machines. This matches the action "You transfer a text document", although truthfully that description is so vague it actually matches all four of the given protocols.
