The default timer settings are 25 minute work sessions with five minute breaks, but you can customize this with the "Change Timer" button. Press "w" to reset the timer and start working or "b" to reset and start a break. Then enter "y" to confirm.
The Pomodoro technique is a method for studying that I find very helpful. It consists of a work session of about 25 minutes followed by short breaks in which you check of one "Pomodoro" and record the tasks that you accomplished. After four of these it is recommended that you take a longer break of about 20 or 30 minutes. Feel free to remix this and add/remove features to your liking.