How to create ARM template file and parameters to install software

Hi @alkohli - No issue to report - just asking for assistance :)
I am looking to automate the installation of Sophos anti virus software when deploying new hosts to AVD.
Because of the way sophos works I cannot install on my customised image as such I am thinking of installing sophos when I deploy a VM to the host pool. I can now see an option to link an ARM template file and template parameter file to the deployment (see pic) but I am not sure how to configure these files, I cannot find an example anywhere. I even opened this [[Q&A]](https://docs.microsoft.com/en-us/answers/questions/611259/azure-avd-add-vm-to-host-pool-custom-config.html) but not getting far.
Would you be able to help me please?
Many thanks