Read the official Pomodoro Technique overview. A Pomodoro is 25 minutes of focused work followed by a 5-minute break. After 4 Pomodoros, take a 15-30 minute long break. Key rules: Pomodoros are indivisible—no interruptions; if interrupted, void and restart; protect your Pomodoro by informing/negotiating external distractions; break tasks larger than 5-7 Pomodoros into smaller ones; combine tiny tasks into one Pomodoro.
Visit pomodorotechnique.com and review the Quick-Start Guide (free download via Gumroad). Note the five stages: Planning, Tracking, Recording, Processing, Visualizing.