I don't know that why Lord Shiva is considered as the destroyer of the world? Please somebody answer my question!
Shiva is not the destroyer. This confusion springs up because of adopting a lens of Judeo-Christian religion into Sanatana Dharma.
“Shiva is often mistranslated as 'the destroyer' and assumed to be the antithesis of Brahma, the 'creator' and Vishnu, the 'preserver'. We have seen that Brahma is not a Creator-God in the Judeo-Christian sense, nor is Shiva a destroyer-God as many writers today think. Shiva might perhaps best be described as a transformer who moves humanity and the universe forward in the evolution of consciousness. This evolution entails dissolution of the falsely constructed mental frame of reference (nama-rupa) and is different from destruction. The transformation brought by Shiva is a deconstruction process that has been misconstrued as destruction. The physical and material dissolution may also be seen as the end of a cycle – making room for fresh manifestation in the same way as one season gives way to another. The tradition emphasizes continuity, making “every apparent destruction, in fact, a transformation. Shiva is therefore also described as the lord of dance and of yoga, enlightenment and mysticism, and this is why he inspires so much more devotion than he would if he were thought of simply as 'destroyer'.”
The above is an excerpt from the book 'Being Different' by Rajiv Malhotra.
Also, I would like to mention the translation done by Monier Williams (a professor of Sanskrit in Oxford University) in his Sanskrit-English dictionary.
He gives 'in whom all things lie' as the primary meaning of Shiva, derived from the root śi. Other important meanings of the word are 'auspicious', 'kind', and so on. Shiva is also 'a-kala', i.e., beyond time, and 'sada-shiva', the eternal who stays on despite and beyond destruction.