any course to learn how to develop applications for android devices?

Answer 1

I'm using Udacity to learn about android development. If you're a beginner for android development you could start here:
https://www.udacity.com/course/android-basics-user-interface--ud834
Udacity is also available on Play store:
https://play.google.com/store/apps/details?id=com.udacity.android

Answer 2

There aren't any courses on Sololearn specifically about that, so you may need to look online for tutorials outside of Sololearn for that. At the moment, Android Studio seems to be one of the more popular choices developers use when developing applications for Android so I would recommend checking it out. It uses Java/Kotlin for the coding portion of it, so I would recommend checking out both languages for that. Sololearn does offer a complete Java course, but the Kotlin course is still in development at the moment so you may have to look for other sources for learning it. Kotlin has begun to be a very popular option for coding with Android Studio, so it would be worth checking out.

Hope this helped! d: