Your application files live your app's public folder, also called the web root directory.
When you SSH/SFTP in to your server as your app's system user, this directory will be located here, where APPNAME is the name of your app:
apps/APPNAME/public
If you have logged in as the root user, then you can access your app's web root directory at its absolute (full) path, where SYSUSER is the name of your app's system user, and APPNAME is the name of your app:
/srv/users/SYSUSER/apps/APPNAME/public
This is where you put all of the files needed for your app.
You might have seen this directory called public_html, htdocs, httpdocs, httpsdocs, www, or wwwroot in other hosting environments.