This is a simple how to use F-Droid App Store for Android users everyone can practice. I hope this helps Ubuntu users who have Android devices!

About F-Droid

What is F-Droid? F-Droid is an Android app store which provides Free Software apps friendly and securely. To use F-Droid, one must install it first from the website https://f-droid.org. The difference to the original Play Store is, in F-Droid, an Android user will never find proprietary software nor malware apps. The background behind F-Droid is the Free Software Community, which engages in the world wide Free Software Movements since long before Android was born, the same background with Ubuntu and GNU/Linux. That's why F-Droid to any Ubuntu user will feel like home and very familiar. F-Droid is not only available for Android, but also for Replicant OS.

Getting F-Droid

• Pick up your Android phone.
  
• Open its web browser.
• Go to www.f-droid.org.
• Tap 'DOWNLOAD F-DROID' button on that webpage.
• You got a file named f-droid.apk.
• Tap the apk file and install the application.
• F-Droid installed. 
  

Run F-Droid

• Once installed, F-Droid will appear among your apps.
• Run F-Droid. 
• On the first run, F-Droid will download some data from the internet ("repository").
• Once finished downloading, F-Droid is ready.

To Get Even More Apps

• Run F-Droid.
  
• Go to F-Droid's settings and enable Guardian Project repositories if you want privacy apps like Tor Browser. 
• Enable Archive repositories if you want old versions of apps e.g. if your phone is old.
• Refresh the repository.
  

Search and Install Apps

- VLC, everyone's media player
- NewPipe, the best youtube browser & downloader
- DiskUsage, see your folders disk usage ranking
- Telegram FOSS, the fast and popular messaging app
- Document Viewer, the enjoyable PDF reader
- Apple Flinger, a game similar to Angry Birds
- Tor Browser, your secure internet explorer

There are plenty of apps and games in F-Droid. Those above are examples of apps and game you can enjoy. To install one, for example, Telegram FOSS:

• Open F-Droid. 
• Tap search button.
• Type the app name 'telegram' without quotes.
• You find search results and one among them is Telegram FOSS.
• Tap Telegram FOSS, it opens the full description.
• Tap Install button.
• Wait for a while the download process to take place.
• Tap Install once again. 
• The app installed successfully.
• Run the app from your app menu.

Find Your Friends

Finally, F-Droid and its apps users gather around several communities, mostly related to Free Software Movements, for example at Mastodon (social network) and at F-Droid's own online forum. They also participated in European's conference FOSDEM like this public presentation. That's all and I hope you enjoy F-Droid!