The Present tenses are - the Present Simple, the Present Continuous, the Present Perfect, the Present Perfect Continuous. In brief the difference is in the following: The Simple is responsible for the actions which are repeated, habitual, regular - marked by adverbs always, often, usually ... and alike. Ex. I go to the gym every day. He usually reads fantasy.
The Continuous - actions which are going on at the present moment or moment of speaking (you can look at your watch and fix the time of the action): What are you doing (at the moment of our talking)? - I am reading.
The Perfect: the action is comlete just by the moment of speaking. - I have just written a new poem. Listen!
The Perfect Cont.: the action started in the past, was in progress for some time and is complete by the moment of speaking. I have been writining this poem all my life. Listen!
** But this is a VERY brief account. There're a lot of more subtle things about Tenses.