Before going to deep into Ionic we need to know about that What is Ionic? so the answer is Ionic is an HTML5 based mobile application development framework, which is used to develop hybrid mobile applications. Here for newbies hybrid mean develop an one application for different platform's such as Windows, Android, IOS platforms.
In general hybrid applications are small websites which are running in browser shell.
We can say that Ionic is the front-end UI framework that will handle look and feel and user interfaces for our applications. Ionic framework provide very native-styled mobile interface elements and layout for our applications and it gives very powerful ways to build mobile applications.
So by Ionic official documentation "Since Ionic is an HTML5 framework, it needs a native wrapper like Cordova or PhoneGap in order to run as a native app. We strongly recommend using Cordova proper for your apps, and the Ionic tools will use Cordova underneath."
Structure of Ionic Applications
Now that, you have great understanding about ionic, and you are ready to start building your first application in ionic framework. Before building our first application we need to setup ionic in our local machine. To install ionic and its dependencies read my article How to Setup Ionic and its dependencies.