I recommend you to read the primer again. But this time read the recommended reading on the links at the beginning of the primer. I can help you, but it would be better for you to read it one more time. Then ask questions of what you don’t understand of the guide and primer; I will help you with the rest.
Testing Today @search([d] today)
That would not work. The tag is there to let the search engine know what you are looking for. Things due today? Before today? After today? (=<>). Putting dates inside tags are also helpful with organizing things. I usually use @due, @recurring, @bill, @calendar @event. I do this because then I can automatically update my calendar or events using those tags and a script I modified. It is found in the Wiki, but here is the link, Script to update Calendar and Events in OS X using Taskpaper tags
Now, you you want things due today and not done, use something like this,
@due = [d] today except @done
You will notice that it if the parent is marked as “@done”, but the task or project “@due” is not tagged with “@done”, that will still appear. If you read the documentation, you can find that “Item Paths” is what you need. So,
@due = [d] today except @done//*
Will show different results. Read the docs, and ask me some questions.