Tachiyomi has become the best opensource manga reader available for Android Phones and Tablets today. Its clean UI and customization options provide you to easily read manga from online sources and download them to read offline.
Once you downloaded and installed Tachiyomi app on your android device, you have to install Tachiyomi extensions to start reading. Tachiyomi extensions allow you to get mangas from their sources. Simply extension is the part that connects the Tachiyomi app with manga sources. An extension can contain multiple sources. Usually, extensions come in .apk format where you can download and install. But the easiest way to install in using the Tachiyomi app to get easily installed.