what is linear supply function? pls. explain with  example 

Tanu, follow the below link and if still you have any doubt, then do let us know about the same explicitly.
https://www.meritnation.com/ask-answer/question/a-straight-line-supply-curve-is-drawn-indicating-a-non-lin/the-theory-of-the-firm-under-perfect-competition/9626957