info path in share point online and what is the use of it?

Hi Srinivasa Reddy, Read this.

One common use of InfoPath is to integrate it with Microsoft SharePoint technology. InfoPath forms can submit to SharePoint lists and libraries, and submitted instances can be opened from SharePoint using InfoPath Filler or third-party products. Alternatively InfoPath Forms Services enables a browser-enabled InfoPath form to be hosted on a SharePoint installation and rendered as an HTML page with  

https://stackoverflow.com/questions/3958068/what-is-infopath-and-how-to-use-in-sharepoint