A scene-setting cascade of noun phrases. 整えられた is the passive of 整える ('to arrange, to order'), used attributively: 'the long tables that have been arranged.' いくつかの is the indefinite number modifier 'some, several.' パイプ椅子 ('pipe chairs') are the folding chairs with metal-tube frames commonly used in Japanese meeting rooms. 貼られている is the passive-state of 貼る ('to paste, to stick') — 'are (currently) pinned.' The sentence is almost nominal, building a visual inventory rather than making claims.