ADJECTIVES – are describing words. They describe NOUNS (people and things)
they are either before the noun, (She is a beautiful girl), or connected by a linking verb (the girl is beautiful)
If there are more than one adjective before a noun, they are separated by a comma and the size is before the colour, if this is the example (the big, black dog)

ADVERBS – are words that describe verbs (how?). “-ly” is added after the adjective to make it an adverb:
She writes beautifully. they played nicely.
Not all adverbs have the -ly at the end. E.g. She walks fast. My mother cooks well.