Read the full lesson at http://blog.mymusictheory.com/2014/how-to-compose-a-canon-or-round-easy-composition/
How to write a canon (or “round”) using Musescore.(Musescore can be downloaded for free from www.musescore.org).
A canon is a melody which is played by two or more instruments at staggered intervals. Because each part starts the melody at a slightly different time, harmonies are created by the combination of sounds. Writing a canon which works is very easy – you just need to plan in advance what chords you want to build the canon around.
Well-known canons are “Frere Jacques” and “Three Blind Mice”. They are built on very simple chord patterns. You can easily choose a slightly more complicated harmonic structure for your canon, making some really nice harmonies.
This video shows you how to compose a canon using Musescore, which is an easy-to-use music publishing software freely available to download. However, you can use any music software you like, or none at all if you prefer!