diff --git a/Android/2021_05_11_AndroidClass-2/README.md b/Android/2021_05_11_AndroidClass-2/README.md
index d969172..9c62ff0 100644
--- a/Android/2021_05_11_AndroidClass-2/README.md
+++ b/Android/2021_05_11_AndroidClass-2/README.md
@@ -37,3 +37,4 @@
- Create a simple single activity project which supports app language change using the string resources files (`strings.xml`)
- Try implementing `RecyclerView` (it is very similar to `ListView`).
- Try to change your app's icon.
+- Learn what is `SharedPreferences`.
diff --git a/Android/2021_05_13_AndroidClass-3/README.md b/Android/2021_05_13_AndroidClass-3/README.md
index 25293fa..b4a33e4 100644
--- a/Android/2021_05_13_AndroidClass-3/README.md
+++ b/Android/2021_05_13_AndroidClass-3/README.md
@@ -9,3 +9,21 @@
## Class Content:
+
+- [Services](https://developer.android.com/guide/components/services)
+- JSON parsing:
+ - [Volley](https://developer.android.com/training/volley) for network requests
+ - [JSONObject class](https://developer.android.com/reference/org/json/JSONObject)
+ - [Android JSON Parser Tutorial](https://www.javatpoint.com/android-json-parsing-tutorial)
+ - [Online JSON Viewer](http://jsonviewer.stack.hu/)
+- Firebase:
+ - [Firebase Console](https://console.firebase.google.com/)
+ - [Firebase Realtime Database documentation](https://firebase.google.com/docs/database)
+ - [Steps to configure](https://firebase.google.com/docs/database/android/start)
+ - [Connect to Firebase](https://developer.android.com/studio/write/firebase)
+ - [Firebase Auth documentation](https://firebase.google.com/docs/auth)
+ - [Setup steps with FirebaseUI](https://firebase.google.com/docs/auth/android/firebaseui)
+ - [Using phone number](https://firebase.google.com/docs/auth/android/phone-auth)
+- Notifications:
+ - [Notifications](https://developer.android.com/guide/topics/ui/notifiers/notifications)
+ - [Create a Notification](https://developer.android.com/training/notify-user/build-notification)