Estimates vary from about 450,000 words to over a million, but many are not widely known or used. The number you should know to communicate is much less. Remember that with so many words, native speakers also learn new words & forget the ones they don't use. How does one remember them? Use. Use them. Use them often. Read them, frequently. Read them regularly. English is well equipped with shades of meaning. Get into a crowd that uses many words & you will use many words.

Read them day by day, not word by word but sentence by sentence