AngularJs is not different from other application. It also starts application with bootstrap process.
Following operation happens inside AngularJs bootstrap process.
Load application module. Create dependency injector and load dependencies. Compile HTML and create scope for application.
All these steps happens inside angular.js scripting file. therefore we need to include it first. we can include it inside HEAD tag or at end of BODY tag.
Note: Adding angular.js file at end of body tag will allow browser to load of HTML elements without any delay and afterwards load angular.js and begin bootstrapping process.
You can get angular.js source file from https://code.angularjs.org/
AngularJs bootstrap process happens on document ready event.
lets see the simple AngularJs example.