You can search for lyrics from a list of lyrics websites without leaving the app or go to popular search engines. If you have a Scrobbler like https://f-droid.org/packages/net.jjc1138.android.scrobbler or https://f-droid.org/packages/com.adam.aslfms installed then JLyr can detect what you are listening to and search for the lyrics automatically. The app is also able to detect what the stock Music app (https://f-droid.org/packages/com.android.music) is playing, without a Scrobbler.