The purpose of the "exported" is to let other apps have access to a service.
For example, \android-sdk-windows\samples\android-8\SampleSyncAdapter\AndroidManifest.xml
<service
android:name=".authenticator.AuthenticationService"
android:exported="true">
<intent-filter>
<action
android:name="android.accounts.AccountAuthenticator" />
</intent-filter>
<meta-data
android:name="android.accounts.AccountAuthenticator"
android:resource="@xml/authenticator" />
</service>
<service
android:name=".syncadapter.SyncService"
android:exported="true">
<intent-filter>
<action
android:name="android.content.SyncAdapter" />
</intent-filter>
<meta-data
android:name="android.content.SyncAdapter"
android:resource="@xml/syncadapter" />
<meta-data
android:name="android.provider.CONTACTS_STRUCTURE"
android:resource="@xml/contacts" />
</service>
The source code that matches with these services is then found in your samples folder at
\android-sdk-windows\samples\android-8\SampleSyncAdapter\src\com\example\android\samplesync\authenticator\AuthenticationService.java
and
\android-sdk-windows\samples\android-8\SampleSyncAdapter\src\com\example\android\samplesync\syncadapter\SyncService.java
An example of using this might be located at...
\android-sdk-windows\samples\android-8\SampleSyncAdapter\src\com\example\android\samplesync\client\NetworkUtilities.java (3 hits)
Line 63: "https://samplesyncadapter.appspot.com";
Line 238: // Succesfully connected to the samplesyncadapter server and
Line 287: // Succesfully connected to the samplesyncadapter server and