Electronic Circuits and Projects Forum

You're question is overly simplistic.
You've not provided much information other than they are using CW (morse).

What kind of homework is this ? You would not be asked to build a radio transmitter in a college course without having been taught some basic high school physics and electronics on oscillators and amplifiers.

The Dick Smith Funway 1 electronics book has just such a transmitter and receiver in it.
These books are common in Australia and NZ. They can be hard for somebody not in Australia to acquire. Placing a wanted ad on somewhere like vkham.com is your best chance. (there aren't any on ebay at the moment) It is a very basic beginners electronics books and the article on that circuit has a very good novice explanation of radio waves and radio circuits.

A quick search for "crystal radio" will yield results and a circuit you can build and understand.