Gesture Detector and the Inkwell class are sometimes confused with each other.
What differentiates an inkwell from a gesture detector 😕? let's try to demystify that.

Leggo! 🚀

What is a gesture detector 😕?

According to flutter's official documentation, it says a gesture detector is a widget that detects gestures, and it also attempts to recognize gestures that correspond to its non-null callbacks. By corresponding to non-null callbacks, it responds to intent passed to it, but it is a non-visual widget.
You can visit pub.dev to read more

And an Inkwell ❓

pub.dev defines an inkwell as a rectangular area of a Material that responds to touch, it further explains that the InkWell widget must have a Material widget as an ancestor. The Material widget is where the ink reactions are painted, this matches the material design premise(border/ boundary) wherein the Material is what is reacting to touches by spreading ink. This already indicates that an inkwell has some visual properties when compared to a gesture detector
( Difference already established 💡).

Now let's get practical about this...

Let's jump into some code writing to further cement our knowledge about a gesture detector and an inkwell. Don't be scared, it's very basic code okay 😏?
let's create a main.dart file and write this piece of code in it

void main() {
  runApp(const MyApp1());
}
class MyApp1 extends StatelessWidget {
  const MyApp1({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyApp(),
      debugShowCheckedModeBanner: false,
    );
  }
}
class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
  int index = 0;
  var random = Random();

  List myColors = [
    Colors.blue,
    Colors.blueGrey,
    Colors.amberAccent,
    Colors.tealAccent,
    Colors.deepPurpleAccent
  ];

  void changeColor() {
    setState(() {
      index = random.nextInt(4);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.fromLTRB(50, 250, 50, 100),
        child: Center(
          child: Column(
            children: [
              GestureDetector(
                onTap: () {
                  Navigator.of(context).push(MaterialPageRoute(
                      builder: (context) => const NewScreen()));
                },
                child: Container(
                  height: 150,
                  width: 150,
                  child: const Center(
                      child: Text(
                    'Tap',
                    style: TextStyle(fontSize: 30),
                  )),
                  decoration: BoxDecoration(
                      color: Colors.redAccent,
                      borderRadius: BorderRadius.circular(20),
                      border: Border.all(color: Colors.black)),
                ),
              ),
              const SizedBox(
                height: 50,
              ),
              InkWell(
                splashColor: Colors.limeAccent, highlightColor: Colors.amber,

                onTap: changeColor,
                child: Container(
                  height: 150,
                  width: 150,
                  child: const Center(
                      child: Text(
                    'Tap',
                    style: TextStyle(fontSize: 30),
                  )),
                  decoration: BoxDecoration(
                      color: myColors[index],
                      borderRadius: BorderRadius.circular(20),
                      border: Border.all(color: Colors.black)),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
}

your results should look something like this

Now let's create our NewScreen page, create a new_screen.dart and write this there

class NewScreen extends StatelessWidget {
  const NewScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: MediaQuery.of(context).size.width,
      height: MediaQuery.of(context).size.height,
      decoration: const BoxDecoration(color: Colors.cyanAccent),
      child: const Center(child: Text('Welcome to a new Screen', 
      style: TextStyle(color: Colors.black, fontSize: 20),
)
),
    );
  }
}

You should be having something like this by now 👇🏽 📌Notice the yellow splashes when you tap on the inkwell (I mentioned that earlier as ink reactions), the same doesn't happen when you tap on the gesture detector.
From a basic standpoint, this explains the differences between an inkwell and a gesture detector.
However, as you explore these two widgets you would understand their differences from a more practical view.

via GIPHY