I need to know what is rich snippets and its effect on SEO?

Some one know about wordpress plugin for rich snippets I have tried several but it does not seem to be working for me

Well, it looks like most of the part has already been covered by @tdrosiadis and to understand what rich snippets is? I think I can came up with little defnition- It's about providing search engines an additional information about your website, so it can display more useful information to people searching.

Rest of the things are Ditto as @tdrosiadis !

@tdrosiadis and @kelly burby thanks to giving me this useful information.

Thanks a lot! Feel nice to help out. You can consider giving a solved flag to my answer also if you feel like :)

I'm a huge proponent of rich snippets and microdata. I encourage you to read and implement http://schema.org/ microdata on your site. It helps with SEO and also with site accessibility.