1st & 2nd Fragmeant

 Main Activity XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity"
    android:layout_margin="10dp"
    >

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="First Fragment"
        android:textSize="20sp"
        android:textStyle="bold"
        />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Second Fragment"
        android:textSize="20sp"
        android:textStyle="bold"
        />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Third Fragment"
        android:textSize="20sp"
        android:textStyle="bold"
        />


    <FrameLayout
        android:id="@+id/frameLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />


</LinearLayout>

 Main Activity JAVA

package com.rakibshah.fragment;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import com.FirstFragment;
import com.SecondFragment;

public class MainActivity extends AppCompatActivity {

    Button button1, button2, button3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button1 = findViewById(R.id.button1);
        button2 = findViewById(R.id.button2);
        button3 = findViewById(R.id.button3);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                FragmentManager fManager = getSupportFragmentManager();
                FragmentTransaction fragmentTransaction = fManager.beginTransaction();
                fragmentTransaction.add(R.id.frameLayout , new FirstFragment());
                fragmentTransaction.commit();

            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                FragmentManager fragmentManager = getSupportFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.add(R.id.frameLayout, new SecondFragment());
                fragmentTransaction.commit();

            }
        });

    }
}

Create Fragment File

Com > NEW > Fragment > Fragment(Blank)

First Fragment XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.FirstFragment"
    android:background="#88B6BC"
    android:orientation="vertical"
    android:padding="15dp"
    >


    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="1st Fragment"
        android:textSize="40sp"
        android:textStyle="bold"
        android:textColor="#FFFFFF"
        />

</LinearLayout>

First Fragment JAVA

package com;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.rakibshah.fragment.R;

public class FirstFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View myView = inflater.inflate(R.layout.fragment_first, container, false);

        return myView;
    }
}

 Second Fragment XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="#DD4D4D"
    tools:context="com.SecondFragment">



    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="2nd Fragmeant"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="#FFFFFF"
        android:layout_gravity="center"
        />

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

Second Fragment JAVA

package com;

import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;

import com.rakibshah.fragment.R;


public class SecondFragment extends Fragment {

    Button button;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View myView = inflater.inflate(R.layout.fragment_second, container, false);

        button = myView.findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Toast.makeText(getContext(), "Hello", Toast.LENGTH_LONG).show();

            }
        });

        return myView;

        }

   }