I am a skinny vegetaria man and wants to gain health. But it doesn't matter how much I eat. I remain same. Please give some tips for gaining health.

Protein. As long as you are working out / physically active, you can help gain mass with a protein supplement (either powder-->shake type or bar). However, it is easier to gain fat, which is not desirable. Not everyone is "big, " it may be much wiser to accept you for you.