Beginner help with a Deployment with IaC

I'm a developer who works mainly with developing applications, and while I have handled pushing code to production, my involvement with deplotments is limited to raising PRs and that's about it. While I understand cloud basics, I really do not have a practical understanding of devops.

I've been assigned (against my will) to take point on a PoC that involves deploying something to Azure with literally zero context. All I know is that it involves Terraform, IaC, GitHub Actions, Azure portal and a GitHub Repo. I've brushed up on all these, but I'm unable to understand how to link all of them together practically.

Also, from what I have seen, one of the roadblocks is that in that repository, there's both code related to the IaC aspect as well as the application. Can someone explain why this would be a blocker, some of the potential issues this can cause, and how this can be handled? I've only understood the permission aspect, but not any other issue that can be a blocker.

If anyone has any suggestions on other topics I should know, any resources I could use or any advice in general, it'd be helpful. I really don't have any option but to do this task, and I need to be a little proactive and raise solutions, but I don't know enough and am lost.