Synonyms are words that have the same, or almost the same, meaning as another word. You can say an “easy task” or a “simple task” because easy and simple are synonyms. You can say Hong Kong is a “large city” or a “metropolis” because city and metropolis are synonyms.
However, it is important to remember that not all pairs of words in the English language are so easily interchangeable. The slight but important differences in meaning between synonyms can make a big difference in your writing. For example, the words boring and insipid may have similar meanings, but the subtle differences between the two will affect the message your writing conveys. The word insipid evokes a scholarly and perhaps more pretentious message than boring.
The English language is full of pairs of words that have subtle distinctions between them. All writers, speakers and beginners alike, face the challenge of choosing the most appropriate synonym to best convey their ideas. When you pay particular attention to synonyms in your writing, it comes across to your reader. The sentences become much more clear and rich in meaning.