For iOS / iPhone
Click this link, or search for "RAYVN" in the App store. Click the download icon. This is a free download, and the app should start to download and install automatically. If you are not logged in with your Apple ID, you might be asked for your Apple ID username and password before downloading the app. If you haven't downloaded apps before on your phone, you can read this article from Apple.
Click this link, or search for "RAYVN" in Google Play on your phone. Click the on the download icon, and the app will start to download and install on your phone. If you are not logged in to your Google account, you will be asked for your Google/Android username and password.
After the app has been download, you should see the icon of the RAYVN app on your phone.
Now you are ready to log in.