Widget are reusable components

                    import 'package:flutter/material.dart';



void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Functional Widget Example'),
        ),
        body: myFunctionalWidget(),
      ),
    ),
  );
}


Widget myFunctionalWidget() {
  return Container(
    color: Colors.blue,
    child: Center(
      child: Text(
        'Hello, Stateless Functional Widget!',
        style: TextStyle(
          fontSize: 18,
          color: Colors.white,
        ),
      ),
    ),
  );
}

Example

                     //widget 1
                    Widget circleRow() {
                      return Row(
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: [
                          circleIcon(),
                          circleIcon(),
                        ],
                      );
                    }




 //widget 2
  Widget circleIcon() {
    return Icon(
      Icons.circle,
      color: Colors.white.withOpacity(.5),
      size: 10,
    );
  }



  //widget 3
  Widget customDrawer() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: [
        Card(
          elevation: 20,
          color: Colors.white.withOpacity(.1),
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
          child: Container(
            height: 40,
            width: 40,
            padding: const EdgeInsets.symmetric(vertical: 10, horizontal: 10),
            decoration: BoxDecoration(
                color: Colors.white.withOpacity(.1),
                borderRadius: BorderRadius.circular(10)),
            child: Column(
              children: [circleRow(), circleRow()],
            ),
          ),
        ),
        ClipRRect(
          borderRadius: BorderRadius.circular(20),
          child: Card(
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(10),
            ),
            child: const FlutterLogo(
              size: 35,
            ),
          ),
        ),
      ],
    );
  }


  //widget 4

  Widget specialCard(AssetImage asset) {
    return Card(
      color: Colors.white.withOpacity(.1),
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(15),
      ),
      child: Container(
        margin: const EdgeInsets.all(10),
        height: 120,
        width: double.infinity,
        child: Row(
          children: [
            ClipRRect(
              borderRadius: BorderRadius.circular(20),
              child: Container(
                height: double.infinity,
                width: 120,
                decoration: BoxDecoration(
                    image: DecorationImage(image: asset, fit: BoxFit.cover)),
              ),
            ),
            const SizedBox(
              width: 20,
            ),
            const Column(
              children: [
                Text(
                  "5 Coffee Beans You\nMust try!",
                  style: TextStyle(
                      color: Colors.white,
                      fontSize: 17,
                      fontWeight: FontWeight.bold),
                )
              ],
            )
          ],
        ),
      ),
    );
  }
}

Usage

Column(
     children: [circleRow(), circleRow()],
),