The best-looking papers are created with LaTeX. Overleaf is a nice tool for creating LaTeX papers that makes collaboration on the paper especially easy. Google Docs is another useful collaboration tool (although the output looks a lot like Word and not as good as LaTeX). You can use any writing tool you like, however make sure that the outcome looks about the same as the example paper, that is, 2-column, 10pt, embedded (apalike) citations, with figures, tables, and equations numbered and in place.
If you worked together with another student on a project, you should write only one paper. Naturally, it will have to be twice as good :-) (but not necessarily twice as long). You will both get the same grade for the paper, unless you specify exactly how the work was divided between the two of you (which is usually really hard to do and not recommended).
It is also fine to use tools such as Grammarly and ChatGPT to improve your writing. But make sure that the end result is accurate and does not include any hallucinations (e.g.\ facts, references, explanations that are not real).
See the class schedule for the due date for papers. They must be emailed as pdf files to risto@cs.utexas.edu; no other formats or methods of turning them in are possible. After I've graded them, I'll set up a time when we can talk about possible future directions of the project etc. If the project turned out really good, you might want to consider submitting it to a conference. We can talk about how to do that when we have the meeting.