I hear that these two website are very helpful for SEO but i don't know how? please share your knowledge and experience regarding these two website that how we can use these sites for our SEO campaign?.
These are social networking sites. The ones you mentioned are popular ones and like others can positively trigger off-site ranking factors the search engine could consider of value to your web pages. There's other good ones too that help with web site promotion. These are not meant to spam repeatedly with keyphrase stuffed lunacy. They are meant to offer the world something of unique value, within your web page content mostly. Lightly influence the search engine into determining your "posts" in social networking sites are credible. Also, a little trick I'm using now is to add a quick access gadget to my Chrome browser so thatr anytime I'm on a web page I want to share socially I can choose the service and write out my blurb quite effeciently, especially when my account(s) log in automatically.
Google+ is a pretty good new social site. There's future power to be generated from that one. Another good one I like is DIGG. That's because I often find my DIGG blurbs on some pretty valuable web pages because DIGG feed a minor part of the web page's contrent, then remains there seemingly permanently, even .gov sites sometimes which is cool with me.