I'll share what worked for me. I did a masters thesis on computational fluid dynamics.
Go to google scholar and find the 'seminal' works in your field, for example say you want to know about aerodynamics, basically every course starts with Anderson's textbook, it has almost 10k citations.
Find the books and papers with tonnes of citations. Those are likely the top books and top people in the field.
Also look for literature reviews and if you search for universities and do 'filetype:pdf' in google, you can find lecture notes and reading lists. Those are all good starting points.
As soon as you know what your topic is, start making it a habit to read research papers, take notes in the margins, highlight stuff. Read papers every week. I was lucky to have a long train ride where I had no phone service for a solid 60mins per day, so I read papers on the train almost every day.
At this point you should know who the key people are and what they are interested in, in your field and topic. For my topic I figured out there are like 20 key researchers in the field, find the ones who are regularly publishing still (last 10 years or so) and read all of their stuff.
You should be forming the 'lay of the land' now and finding patterns in where the gaps are, what future work and next steps are the researchers writing about.
Work with your supervisor to discuss what you learned and narrow down the topic.
So that is the INPUT part of the process covered.
Let's talk about the OUTPUT next.
When I was putting my thesis together, I really didn't want to have to write it all at the end or in the last few months. So my method was to imagine each chapter or so, was a paper of it's own, that built on each other.
As you read you should be putting your literature review together anyway which could be a whole chapter of a thesis. Then the other pieces - introduction, proofs, calculations, experimental design, testing, results, conclusion.
If you start writing bits of it as soon as you get your topic you'll have lots of writing done by the time it comes to publishing, and the challenge is more about editing it down and making it cohesive. Obviously you kind of do the work then write the results, and from there form your intro and abstract to review what you did, and the conclusions to discuss next steps and how to build on your research.
This approach scales from a single paper to a book, and it's mostly about being curious of the current state of the art in your field, building a habit for reading other papers, and figuring out where the gaps could be.
As an undergrad, you're not really expected to contribute new science, so it's fine to pick an existing method and paper and only change a little bit of it, your supervisor will have a better idea of where the bar is set on this point, and what you're expected to accomplish.