Which two things should the Development Team do during the first Sprint?

According to the Scrum Guide, the Development Team should do two things during the first Sprint: develop at least one piece of functionality and create an increment of potentially releasable software. These are the goals of every Sprint, regardless of its order. The other options are not things that the Development Team should do during the first Sprint, as they are either out of scope (such as making a plan for the rest of the project or defining major product features and release plan architecture) or unnecessary (such as analyzing, describing, and documenting requirements for subsequent Sprints).