Hi Priya,
PowerApps is a way of creating apps for Android, iOS and Web using datasources from Dynamics 365 for Finance and Operations. These power apps can be configured using the Windows App or the Builder Browser. The builder provides a range of tools for you to fill up the user interface which includes Forms, Galleries, Control, etc.
The datasources can be SQL databases, Excel worksheets, Data Entities and SharePoint Lists. The data connectors can be integrated with a lot of applications such as LinkedIn or Facebook (There are more than 40+ standard data connectors).
I have created a demo PowerApp as a part of learning, the app displays Inventory on hand for a Android phone (didn't test on other devices).