When I open safari in my iPad it is directed to AppStore

That's probably because you clicked on an ad on one of your other apps. Go to Settings>>Safari>>Clear history & website data.

Is your Search Engine set to Google?

drvikranth wrote:

I Tried this but when I open websites in safari it is getting directed to some unknown sites

Does it happen to all devices that access the internet thru the same router? If so, your router may have been hacked. It's now redirecting traffic to unknown sites. Read this article if you need help:

http://www.consumerreports.org/cro/news/2014/04/5-ways-to-hack-proof-your-router /index.htm