An adjective (نَعْتٌ) describes a noun. In Arabic, adjectives follow the nouns they modify. The adjective and the modified noun (مَنْعوتٌ) should match in gender, number, case, and definiteness.
جاء
الرَّجُلُ
الطَّويلُ
The tall man came.
رَأَيْتُ
الْمَرْأَةَ
الطَّويلَةَ
I saw the tall woman.
See also: