How to use Column Widget
Widget that displays children vertically. To fill the available vertical space, wrap the child widget with Expanded widget. Column does not scroll. If you need a scrolling list, consider using ListView.
How to use AppBar Widget
Widget to implement the material design app bar. The app bar consists of a toolbar and possibly other widgets such as TabBar and FlexibleSpaceBar. AppBar class(API reference) Toolbar Implementation example of leading, title, and actions.