I am submitting a paper and the submission requires a taxonomy or topics . I am not sure about this requirement. Taxonomy with respect to a research paper
In addition to helping the editor, the author's classification aids future potential readers in finding papers of interest. It is a lot like the tags that we apply here to questions.
Arguably this was more useful in the past when full text search was less available, but it is, even now, a quick way to narrow down a search for relevant topics.
This helps the journal find an editor. Example: submitting a paper on the formation of the Solar System to a general physics journal. It's obvious the paper is in astrophysics, but that's it. Do you give the paper to someone who's an expert in planetary science? General relativity? Exoplanets? Stellar physics? This can be really hard to answer for someone who's not in astrophysics.
If the authors give subject tags, it's very helpful, since you can just look up the relevant section in the editorial board's research interest and invite someone there.
The need you to classify your subject using predefined codes specific to your general field. In mathematics we often use the AMS subject classification codes give here. I imagine that your field has its own organisations and one of those have published a catalog of codes.