Learn Arabic (Modern Standard): انغلقت النافذة فجأة.

انغلقت is a Form VII verb. In Arabic, Form VII is often used to make an action happen by itself (intransitive) or to show the result of an action. While a simpler form would mean someone actively closed the window, Form VII means the window closed on its own or just 'became closed'.

What is the purpose of the انـ at the beginning of انغلقت?

The انـ (in-) prefix is the standard starting pattern for Form VII verbs in the past tense. It attaches directly to the three-letter root of the verb, which in this case is غ-ل-ق (related to closing).

Why does the verb end with ت?

The ت (taa) at the very end is the past tense suffix for a feminine subject ('she' or 'it'). It is required here because the subject of the sentence, النافذة (the window), is a feminine noun, as shown by its final taa marbuta (ة).

How does the word فجأة get the meaning 'suddenly'?

فجأة comes from a noun meaning a sudden event or surprise. The double dashes on the final letter are 'tanwin fatha', which adds an 'an' sound. Adding this ending to a noun is the standard way to create an adverb in Arabic, turning the noun into 'suddenly'.