in two words pomodoro technique is self organising technique:
when you are trying to work on the task for 25 minutes with the timer on and without interruptions.
after that you have 5 minutes rest then 25 minutes work cycle starts over.
Usually it requires to have timer that rings after 25/5 minutes cycles.
There are a lot of pomodoro technique timers available,
this website dedicated to Pomodorium - pomodoro technique timer.
See installation/using instructions on right side of the page.