If your site is ranking in SERP then snippets plays a big role in getting clicks because is describes that what page is rally about but search engines are not smart enough to deside what web page is really about .So now all big search engine have decided to use microdata for creating snippets but is you want to search engine creat snippet which really give a user real information about your webpage then you need to add microdata in your web pages.Microdata is just some additional html tags which will not make any difference in look of your web page but tell a search spider that what the web page is about.
To see these data you can visit "http://schema.org" where you can find full documentation , here in this article I will tell you some example but sure I will write some other article to give you full detail about these tags .
Suppose you have a online shopping site and you sell NOIKIA C2-02 then microdata for your page should be like this
<div itemscope="" itemtype="http://example.com/cellphone">
<span itemprop="NOKIA Cell Phone"> NOKIA C2-02 /span>
<meta itemmode="Itemmodel" value="C2-02">
<img alt=" NOKIA Cell Phone e" src="Cell-Phone23.jpg" />
<div itemprop="offers" itemscope="" itemtype="http://example.com/Offer">
<span itemprop="price">Rs. 4000</span>
<meta itemprop="Pricecurruncy" value="INR">
<span itemprop="description">Dual Sim Multimidia Gsm Hand set with FM recording ,2MP camra and socialnetworking support</span>
The main benifit of this tag will be that only your tatgeted visitor will visit your site and you will be in comptition only with your real comptition .In given example if you use Microdata then it will make a clear snippet and then a visitor who is searching for this cell phone will surelly click on your result but is come other user is searching for cell phone technology or cell phone history will not come to your site.Thus you have to compteate only with those who are celling cell phones not with those wo are tellthing about cell phone technology or history and I hope this will help you as an SEO.
I hope this article would be helpfull for you .I will surlly tell all of you detail about most important microdata about most commen sites in my some next post very soon.I you found this article use full do not forgot to share it with your friends.