I am trying to write a reference for a poem that is inside a textbook. Do I reference just the textbook as a normal citation or do I have to include the poet? I'm not sure since it is a poem inside a school textbook.

If you're using MLA Guidelines, go here:

https://owl.purdue.edu/owl/research_and_citation/mla_style/mla_formatting_and_style_guide/mla_works_cited_page_books.html

Scroll down to "A Work in an Anthology, Reference, or Collection" and find what fits.