PRESENT TENSE
Simple Present(describes an action that is happening usually or regularly)
examples: I write books. She writes a letter every day. I study English everyday.
(describes an action that is happening now and may continue)
examples: I am writing a book. She is writing a letter. We are studying English now.
(describes a completed action or an action that began in the past and continued until the present)
examples: I have written a book. She has written a letter. I have studied English in several Canadian cities.
(describes an ongoing action that began in the past)
examples: I have been writing books. She has been writing letters for 2 hours. I have been studying English for two years.
https://www.youtube.com/watch?v=jiZKPwcdn1A