how to call Strings in mainactivity.xml from Strings.xml file

If you want to add the value from strings.xml to TextView in mainactivity.xml , add the following line of code to your xml

android:text="@string/Std_Name"

<TextView
    android:id="@+id/textView1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:layout_marginTop="5sp"
    android:lineSpacingExtra="2sp"
    android:text="@string/Std_Name" // Add this line to your textView
    android:textColor="@color/yellow_dark"
    android:textSize="@dimen/activity_text_size_small"
    android:textStyle="normal" />

Or, if you want to add text from strings.xml to textview from MainActivity.java, add the following code

TextView textView = findViewById(R.id.textView1);
textView.setText(getResources().getString(R.string.Std_Name));

From within an XML layout, you can use the @string/resourceName syntax within the text string to reference a string resource:

android:text="@string/resourceName"

Using the Std_Name string resource from your example, that would look something like this:

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/Std_Name" />

Official documentation for string resources can be found here. You can also find a good example in the Accessing resources from XML section of the App resources overview.

Try this

String myName = getResources().getString(R.string.Std_Name);
String myPhone = getResources().getString(R.string.Std_Phone);

// Then do whatever you want with these values

Call in your Textview text field

android:text="@string/Std_Name"