。
They were trapped inside the house by the storm.
Literal
Storm [by-で] they [topic-は] house [possessive-の] inside [in-に] were-shut-in.
で here marks a light, everyday cause ('because of / by'). 閉じ込める is a compound verb combining 閉じる ('close') + 込める ('put into / pack') — literally 'close [someone] into [a place].' Here in passive form 閉じ込められた, describing the experience from the trapped party's perspective.