I hate to split hairs, but....
A noun clause cannot be fully defined as "when you use a group of words to serve the same function that a noun usually serves in a sentence." That definition doesn't exclude the category of noun phrases.
A phrase is a single word or set of words that can fill a single grammatical slot in a sentence. A noun phrase fills a noun slot, such as the subject slot. A noun phrase can be one word or it can be a whole lot of words:
I am here.
Shelley and Thomas and Buck and I are here.
In the first cause, the one-word subject "I" is a one-word noun phrase. In the second example, the 5-word compound subject (this is "a group of words," too) is also a noun phrase.
A clause is more complex than a phrase. It must at least two grammatical slots filled, that of the subject and that of the verb. The verb slot must include a verb that shows time (or tense). The clause can be independent (which makes it able to stand alone as a sentence) or it can be dependent (which requires it to attach to an independent clause). Noun clauses are always dependent and always fill noun slots within a larger sentence. Finally (I am pretty sure about this), noun clauses must always begin with either the word "that" or with a "wh-" word (why, where, how, etc., including the words "whether" and "if"). In the grammar course that I teach, we talk about "that-clauses" and "wh-clauses," but not everyone uses that vocabulary.
A noun clause is when you use a group of words to serve the same function that a noun usually serves in a sentence. So a noun clause might be "I didn't know that you can sing so well." The noun clause is the last 6 words of the sentence.
Perfect tenses can be used in noun clauses quite easily. Here are examples:
Present perfect tense: I am glad that you have learned to whistle.
Past perfect: Everyone celebrated when they heard that the war had ended.
Future perfect: It is sad to think that he will have died by the time I have children.