How to create a modal in angularJS?

This is something you could do yourself. However, there are plenty of libraries that already do this.

https://pathgather.github.io/popeye/

If you want to pursue yourself then checkout Ben's article on the topic.

http://www.bennadel.com/blog/2806-creating-a-simple-modal-system-in-angularjs.htm

If you want to create an custom modal or dialog box you first need to create a directive and need to control the behaviour of the popup based on an event add a handler that will open the dialog box such as

//Keep this event at the top of your hierarchy.
$scope.$on('OPEN_DIALOG_BOX',function(event,data){
    event.stopPropagation();//stops the event from bubbling up the event chain.
    //add a variable that will show or hide the modal dialog box.
    $scope.hideDialog = true;
    //use data to pass custom message to bind in your html.
    $scope.message = data.message; 
});

//Call this event
$scope.$emit('OPEN_DIALOG_BOX');

or

You can use angular material dialog box.

Or

Use ng-dialog as explained in this blog

FIDDLE FOR THE CODE SNIPPET

I hope this helps.