how do i reconize an adjective? is there any trick?
Adjectives are very simple. An adjective modifies (changes) a noun. A noun is a person, place, or thing. So shirt is a noun. You can pick up a shirt, put it on, take it off. It's a thing.
Black is an adjective. It's a color used to describe a noun.
La camisa Negra = the black shirt
Negra in Spanish is an adjective modifing the noun camisa. Black in English is an adjective modifying the noun shirt.
Other adjectives are: beautiful (the beautiful woman), quick (the quick fox), big (the big dog), happy (the happy child), etc. Remember that in English we put the adjective in front of the noun!