If you are looking to learn terraform in-depth there are two good books on it, first one is
Terraform up and running - Yevgeny Brikman
https://www.oreilly.com/library/view/terraform-up/9781492046899/
This is a good book which discuss live examples and covers production grade code writing as well as how to test your terraform code. It's one of the fantastic resource to start with if you are looking to scale up in terraform.
There is another book from manning called "Terraform in Action". This is another fantastic resource and its a bit in-depth compared to the Yevgeny Brikman's book ( the one referred above ). This has use cases with Go and how to integrate Go and terraform as well as writing a custom provider in Go.
So its a nice guide if you want to know TF at 201/301 levels.
My favourite part in this book, is the live example of coding a three tier architecture using root and child modules. This is a really useful example that is used a lot in your production implementation.
You can checkout the book from manning at
https://www.manning.com/books/terraform-in-action
Please leave your comments on some of the good blogs or books or courses that we can use for terraform learning.
My personal take is, this tool Terraform will continue to grow and will be the market leader, if not already, in the cloud deployment space. So it's going to stay for some time.
I can clearly see in my work, how much we are dependent on terraform to do our configuration updates and creation of resources in the cloud. So migrating away from Terraform, even if you badly wanted to, can be a humongous task.
So this product is worth investing your time and am sure this will pay rich dividends.