To add a Nupedia article to Wikipedia, all you have to do is find the article, copy the contents, and paste it into the appropriate location (whatever you think is appropriate). You should also put up the URL to the original article location in Nupedia; this is an adequate "link back" required by the Nupedia license. For example, have a look at Irish traditional music. The proper text to use at the bottom of a Wikipedia page sourced from Nupedia is: "An earlier version of the above article was posted on Nupedia. This article is open content."
It wouldn't be a bad idea to find this out: How does Wikipedia relate to Nupedia?
See also adding Wikipedia articles to Nupedia.
Question: I'd like to add a new entry to the list on the music page (this was formerly an unbuilt page), for music notation. However, the music page doesn't have a "Edit text of this page" link at the bottom (when this question was written, the music page was unbuilt).
Answer: Sounds like you want to know how to edit a page!
More to the point, whenever you see what looks like a topic, followed by a question mark, just click on the question mark. You did this when you first clicked on the question mark after music. After you clicked on that question mark, you saw a big text box with the words, "Describe the new page here." You probably didn't realize that you could just erase those words and type in whatever you wanted!
I added my "primers" article from Nupedia to wikipedia, which is still an "article in progress". Then I found this page here, and realized there's no URL of that article in Nupedia until it becomes "official". Should I just say "An earlier version of the above article can be found at ."? -- Magnus Manske
Sounds fine. --LMS