We are happy you are here! You are more likely to get a useful response if you are explicit about what your project entails, giving a few more details might help someone give you a nudge in the right direction.
Mark helpful posts with Accept as Solution to help other users locate important info. Don't forget to give Kudos for great content!
If you have no knowledge of Java, then you can consider an alternative: Kotlin. Google is encouraging people to use Kotlin as a viable alternative to Java for Android.
Either Java or Kotlin: get a copy of the IntelliJ IDE (free version). Read the docs and set up a basic project, get it running in an emulation environment. Since you're talking about messaging, you probably need a server, database, and API to talk to it. So you need to figure that out as well.
Please follow-up to let us know how you made out. For good karma, mark a reply as the answer if it helped!