The method, in one paragraph
Francesco Cirillo designed the Pomodoro Technique in the late 1980s around a kitchen timer: pick one task, work for 25 minutes without interruption, take a 5-minute break, and after four rounds take a longer one. The length is not magic. It is long enough to get somewhere and short enough to start without dread, which is why it survived.
What this timer adds
A line to write the task before you start, saved with the block. A countdown you can see from any other tab. A chime and a desktop notification, so you can leave the tab and trust it. And a reason to put the phone in another room: this timer does not run on it, on purpose.
Cirillo, F. The Pomodoro Technique (2006 edition).