error

Your TextView and Button dont appear to include a parent / hierachical layout, such as either a relative layout, a linear layout.

All of your commands at the top above the text view, are not being applied to anything ( i think)

Try something like this

  <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" 
   android:paddingBottom="@dimen/activity_vertical_margin" 
   android:paddingLeft="@dimen/activity_horizontal_margin" 
   android:paddingRight="@dimen/activity_horizontal_margin"
   android:paddingTop="@dimen/activity_vertical_margin" >

  <TextView android:id="@+id/textView1"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:layout_centerHorizontal="true"
   android:layout_centerVertical="true" 
   android:textSize="32sp" />

   <Button android:id="@+id/button1" 
   android:layout_width="wrap_content"
   android:layout_height="wrap_content" 
   android:layout_centerHorizontal="true" 
   android:layout_centerVertical="true" 
   android:text="Button" />

  </RelativeLayout>

Also do note in
tools:context="com.example.driod.MainActivity$PlaceholderFragment" >

you may have spelled droid incorrectly when you typed it into XML ( there is no might to it, you 100% did, just verify that your package name matches what you typed in. if your package has the spelling error "driod" you would be ok. Its worth refeactoring it to the correct spelling though)

Try the above layout, its the same thing you had, just incased in a relative layout so all of the padding at the top has something to apply to.

Your problem, is exactly what it is telling you.

Errors in your XML file keep it from building the project, and as such you are not going to get it to run on the emulator until you fix the Errors in your XML file.

xml document must start and end within the same entity and error parsing the xml ....dont know what they mean

copy and paste your xml file here, and i will help you sort it out.

I also added the line xmlns:android="http://schemas.android.com/apk/res/android"