basically I want to know the way of installing apps
Launch a terminal in the chosen template, and install the software there like you would normally do it in the distro that the template is based on. Shutdown the template afterwards. Shutdown your app qube. Go to settings of your app qube - applications - click refresh. Move the installed app from the left side to the right. Done.
Want to set up “hacking” lab, mainly Kali or Parrot and other to use with the networking to “hack” them, basically I want to run multiples VMs
Install Kali in template manager (it is available as a community template). Create an app qube based on that template. Done.