One-Way Data Binding
ng-bind has one-way data binding ($scope --> view).
Eg., ng-bind="myText" OR {{ myText }}
which displays the scope value $scope.myText inserted into html where myText is a variable name.
Two-Way Data Binding
ng-model is intended to be put inside of form elements and has two-way data binding ($scope --> view and view --> $scope) e.g.
<input name="firstname" ng-model="firstname"/>
When you interact with form element firstname that ng-model interact with $scope.firstname and update the corresponding view automatically by digest loop.
