Hey can anybody tell me that how do I get API key and from where all process and what's the use of API Key ?
If you're referring to a Google API key so that you can check rankings and stuff through an API, they no longer give those out. They stopped issuing them a long time ago. I'm pretty sure the docs for using them are still online at Google. You CAN find them on eBay sometimes. Might want to check there. Search for Google API. Note... They go for a pretty penny typically. If you're looking for an API key for Google Maps, Android, or some other product at Google then the docs are available online as well. Google it.