backend.azurerm - required for system to function property.
local.remote_tfstates.tf - makes possible to reference resources from other landing zones located on the same or upper level.
main.tf - holds a list of Terraform providers with versions to be used withing this add-on. azurerm provider must be kept for system to function property.
outputs.tf - required if you plan to reference execution results from other landing zones. Can be safely deleted if your add-on doesn't produce any outputs.
providers.tf - contains provider configurations.
variables.tf - defines a list of variables that will be used to configure add-on behavior
<resource_type>.tf - contains resources that defines resource you plan to produce with your addon. E.g. helm_release, azure_devops_project etc.
Here's a sample command to run your add-on:
rover -lz /base/path/caf_solution/add-ons/add_on_name \
-tfstate azure_devops-contoso_demo.tfstate \
-var-folder /base/path/configuration/ \
-level level4 \
-env sandbox \
-a apply