who is willing tell me about novella ?

The problem is that you set a word minimum for a novella as 5,000 words and a word maximum of 7,000 words. A fiction work between 5,000 and 7,000 words is not classified as a novella, it is classified as a short story. A novella is frequently classified as being between 7,500 and 40,000 words, with some awards calling a fiction work between 7,500 and 17,500 words a novellete and those between 17,500 and 40,000 words a novella. Above 40,000 words is usually considered a full-length novel.

This wiki article explains the differences between novellas, novelletes, and novels:
Article on Novellas