Since we know that the "Splash Screen" just appears for the few seconds as the app get start so we need to add the time for how much second the splash screen would be shown, so to add  Splash screen in Android app follow the steps mentioned below:-

1) Create a new Activity for Splash screen and name it as SplashActivity, below is the code for the java file of the splash screen where  I have used "Handler.postDelayed" to make the screen appear for the time according to our wish.   .

SplashScreen.java

public class SplashScreen extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_splash_screen);
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {

                Intent intent=new Intent(SplashScreen.this,MainActivity.class);
                startActivity(intent);
            }
        },2000);

    }

2) Add Some content to your SplashScreen's xml file .

activity_splash_screen.xml

<RelativeLayout 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.example.manjeet.fregmentactivitybawa.Java.SplashScreen">

 <ImageView
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@drawable/green"/>

    <TextView
        android:layout_marginTop="34dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="GO GREEN"
        android:textColor="#00ff55"
        android:textSize="30dp"
        android:layout_marginLeft="112dp"/>

</RelativeLayout>

3)Now to move on from one Activity to another and making Splash Screen as your parent Activity do add the SplashScreen.java  Activity in your Manifest file.

Manifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.manjeet.fregmentactivitybawa" >

    <application
        android:allowBackup="true"
        android:icon="@drawable/grasses"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".Java.MainActivity"
            android:label="@string/app_name" >
            </activity>
        <activity
            android:name=".Java.SplashScreen"
            android:label="@string/title_activity_splash_screen" >
<intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>        
</activity>
    </application>
    
</manifest>