What an adjective does
An adjective gives information about a noun: what it looks like, how big it is, where it comes from, how you feel about it.
In English an adjective usually sits directly in front of the noun, or after the verb 'be' and similar verbs such as seem, look, feel and become. Unlike many languages, an English adjective never changes for number or gender: one red door, five red doors.
She lives in a small flat.
Before the noun.
The sea looks cold today.
After a linking verb.
Two tall buildings.
No plural -s on the adjective. Never 'talls'.