"Speak to" and "talk to" imply a conversation between two people. "Tell" doesn't, really. You could TELL someone about your vacation via an e-mail.
In the United States "turtle" is more common than "tortoise". In fact "tortoise" refers to the kind of turtles that live on land, although lots of people loosely use "turtle" to refer to all varieties of the animal--which isn't wrong, really, as "turtle" is in fact the common word for the entire order. See here.
- For Teachers