The simplest definition of an adjective is that it is a word that describes or clarifies a noun. Adjectives describe nouns by giving some information about an object's size, shape, age, color, origin or material.
It's a big table. (size)
It's a round table. (shape)
It's an old table. (age)
It's a brown table. (color)
It's an English table. (origin)
It's a wooden table. (material)
It's a lovely table. (opinion)
It's a broken table. (observation)
It's a coffee table. (purpose)
When an item is defined by its purpose, that word is usually not an adjective, but it acts as one in that situation.
English grammar can be tricky, there are often exceptions to the rules, so you need to be careful. You'll find that English adjectives often end with these suffixes:
Many adjectives also end with -y, -ary, -ate, -ed, and -ing. However, nouns and adverbs can end with -y, lots of nouns end with -ary, nouns and verbs also end with -ate, and verbs also end in -ed and -ing. Remember we said you need to be careful! To work out if a word is an adjective or not, look at it's location in the sentence.
If you come across a word that ends in -y, -ary or -ate (or any other suffix for that matter), and you want to know if it's an adjective, just look at where it is and what it's doing in the sentence. If it comes immediately before a noun, and especially if it comes between an article (a, an, the), a possessive adjective (my, his, her, its, your, our, their), a demonstrative (this, that, these, those) or an amount (some, most, all, a few) and a noun, then it's an adjective.
Adjectives also act as complements. Complements are words that complete the predicate of a sentence when the verb is "be."
As you can see, not all complements are adjectives. In these examples, "tall" and "smart, handsome and rich" are adjectives, but "teachers for five years" and "my best friend" are both noun phrases. If the complement is only one word, there's a good chance it's an adjective. Also if the complement is a list of words, those are probably also adjectives. If an article (a, an, the) or a possessive (my, his, her, its, your, our, their, mine, his, hers, its, yours, ours, theirs) is involved, it's a noun phrase.
When you list several adjectives in a row, there's a specific order they need to be written or spoken in. Native speakers of English tend to put them in the correct order naturally, but if you're learning English, you'll have to memorize the order. It goes like this:
This is the correct order for adjectives that come directly before a noun, and they are separated by commas.
If the adjectives come after the verb "be" as the complement, then the qualifier (the defining word) will stay with the noun at the beginning of the sentence. The adjectives in the complement are separated by commas with the final two being separated by "and."
Adjectives add information and interest to your writing but more adjectives do not necessarily make a better sentence. Use them wisely.