An adverb describes a verb (a 'doing' or 'action' word). Using adverbs helps to make writing more interesting.
For example: The cyclist pedalled furiously down the road.
Most adverbs end in the the letters -ly, but not all of them do, so the best way to check whether a word is an adverb is to see whether it answers the question 'How?'.
How did the cyclist pedal? Answer: furiously.
The girl played the piano well.
How did the girl play the piano? Answer: well.
The word well is an adverb in this sentence even though it doesn't end in the letters -ly.
In the following sentence, the word woolly ends in -ly but it is NOT an adverb because it doesn't answer the question 'How?'.
The woolly sheep munched the grass.
How did the sheep munch the grass? Answer: the sentence doesn't tell us!