how to start
Question: I already have an idea of the story but i don't know how to write or what to write i just start it but i feel as if my work isn't just good enough and i can never write more than three or four paragraphs.Answer:
If you don't know where your story is going, take some time and develop an outline. There are articles on this site to help with that. Or switch to a different story. But don't stop writing.
If you feel your writing isn't good enough, that puts you well ahead of a number of bad writers who are convinced their writing is great and therefore will never improve.
The only thing to do is practise writng, while learning as much about good writing as you can. With practise, self-evaluation, and perhaps feedback from others, your writing will improve.
Most visual artists have to produce hundreds of "practice" drawings and paintings before they get good enough to sell their art. Writing is the same.
Most writers have some insecurity and many never think their writing is great. But as you practise, you will get better, and you will have a harder and harder time finding anything you're doing wrong.
Meanwhile, don't let your desire to be perfect stop you from getting the practice you need to improve.