The four primary functions are
Self Timer,
Interval Timer,
Long Exposure and the
Exposure Count Setting.
Self Timer
Just like the self timer on your camera. Except where most Canon bodies offer either a 2 second delay or a 10 second delay, the TC-80N3 allows you to set any delay (in 1 second increments) up to 99 hours, 99 minutes and 99 seconds. Let's call it 100 hours. That's just over 4 days!
Interval Timer
The Interval Timer can be set to any time period up to 100 hours as well. If you set it to 10 minutes, for example, one exposure will be taken every 10 minutes until either the film runs out or the
Exposure Count limit has been reached.
Long Exposure
This one is easy. It allows you to take time exposures up to (you guessed it) 100 hours in length.
Exposure Count
This fourth and final setting permits you to set the number of exposures that will be taken, up to a total 99. If you set it to 3 exposures you can combine it with an EOS body's auto-bracketing capability.