You can sign up and register for NaNoWriMo or not. Wildcatting is OK.
Some pointers
1) write at least 2000 words a day; the more the merrier during the first week, makes weeks 3 & 4 easier. You need 175 pages or 50,000 words. Deadline—and I do mean dead line—is Nov 30.
2) find a NaNoWriMo group in a coffeshop near you. Writedriver captains (AKA Municipal Liasons) will flagellate and goad slaphappy and punchdrunk participating procrastinators with proverbial whips and spurious words. Oh my Captain...
3) never revise
4) don't worry about plot or storyline. That comes during revision.