Android XML file

1. What does it mean for  "tools:context="com.abc.passingdata.MainActivity"  ? (sample 1)
2. What does it mean for the following XML statement ? For "action", does it refer to the corresponding java class. How does "category" defined in sample 2 ? Any special meaning ? Thx

            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />  

           <action android:name="com.abc.usingintent.SecondActivity" />
            <category android:name="android.intent.category.DEFAULT" />
   
SAMPLE 1
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:orientation="vertical"

    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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.abc.passingdata.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Welcome to the Second Activity"
        android:id="@+id/textView" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click to go to Main  Activity"
        android:id="@+id/button"
        android:onClick="onClick"/>

</LinearLayout>

SAMPLE 2
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        <activity android:name=".MainActivity">
            <intent-filter>
               <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".SecondActivity" >
        <intent-filter >
            <action android:name="com.abc.usingintent.SecondActivity" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>