What are some good websites to use to help me with writing a master's essay/thesis or a dissertation?

Are you looking for format? Thesis paper format in APA I would recommend Purdue Owl or APA. I have included the links to those two sites: https://owl.purdue.edu/owl/research_and_citation/apa_style/apa_formatting_and_style_guide/apa_sample_paper.html
https://apastyle.apa.org/style-grammar-guidelines/paper-format/sample-papers
Another site you may want to visit for dissertation paper would be
https://apastyle.apa.org/style-grammar-guidelines/paper-format/student-annotated.pdf