Short answers, pulled from the story.
The word zazen appears in Japanese Buddhist texts, but its roots stretch back to the Chinese term zuòchán found in early sources like the Dhyāna sutras. The famous translator Kumārajīva lived between 344 and 413 CE when he translated a work called Zuòchán sān mēi jīng.
Japanese Rinzai schools typically combine zazen with the study of koans as a primary method. In contrast, the Sōtō school makes less or no use of koans and prefers an approach known as shikantaza where the mind has no object at all.
Practitioners sit together in a meditation hall usually referred to as a zendo. Each person sits on a cushion called a zafu placed on a low flat mat called a zabuton.
Dainin Katagiri Roshi taught watching the breath while Shunryū Suzuki taught counting the breath. Others like Kōshō Uchiyama and Shohaku Okumura taught neither counting nor watching the breath.
The beginning of a period is traditionally announced by ringing a bell three times known as shijosho. The end comes when ringing the bell once or twice called hokensho.