Many of the widgets in Flutter are descended in some way from a platform-specific guideline: Material Design or iOS Cupertino. This helps the developer to follow platform-specific guidelines in the easiest possible way.
If you do not know the Material Design or iOS Cupertino guidelines, then it's a good time to get to know them:
Material Design: https://material.io/guidelines/material-design/introduction.html.
iOS Cupertino: https://developer.apple.com/design/human-interface-guidelines/ios/overview/themes/.
Material Design: https://material.io/guidelines/material-design/introduction.html.
iOS Cupertino: https://developer.apple.com/design/human-interface-guidelines/ios/overview/themes/.
Flutter, for example, does not have a Button widget; instead, it provides alternative button implementations for Google Material Design and iOS Cupertino guidelines.
We are not going to get deeper on each widget property or behavior, as these can be easily studied by running examples or visiting the docs. Also, you can check the Flutter Gallery app on Google Play (https://play.google.com/store/apps/details?id=io.flutter.demo.gallery) to find a short and cool demonstration of the available widgets.