When you want to use existing audio files in an Ardour session, the first choice you need to make is whether you want to bring the files in as tracks or as new regions. Consider the two following scenarios:
you have an 8 track recording of existing material, with 1 audio file per track
you have a sample library containing 500 small audio files
In the first case, your goal is probably to have 8 tracks (at least), with each track containing a single audio file. In the second case, its a lot more likely that you simply want to be able to use any of the samples easily, but do not want any tracks created as a direct result of the import/embed. It is very important that you understand this distinction: many new users think there should be a "simple" way to import existing audio without understanding that the goal of importing/embedding is not always the same.
Ardour provides two different options when importing. You can import/embed audio files as new tracks, or you can import/embed them into the region list, where they will be available as regions to put into new or existing tracks. You can also insert import/embed audio files directly into an existing track.