Yeah the site doesn't look through to see if you have the same word repeated 50,000 times or anything like that. You can copy+paste your story into the site and it'll calculate your total, but I also think they have a way to manually update yourself without having to do that, so you can lie about your word count. And for some people, it probably does hurt their pride but the coupons for different things once you win are really good. I even thought about cheating myself this year, haven't decided yet XD I'm actually competing but my aim is for around 30,000 words, not 50,000, so even though I'll win my person goal, it doesn't count as winning NaNo so I can't get the prizes v.v
By getting to 50,000 words and updating your word stats on the NaNo site. Some people actually do it or some people just cheat abd paste in different things until it tells them 50k lmao.
Afterwards you can basically do whatever you want. NaNo themselves like to call December and January the editing months, where they encourage participants to go over what they wrote and edit it for content, which some people do. Some people put their stories online, and some people continue their novels until it's complete (if they didn't complete it during November) and self-published them. Like Airi. was saying, when you win NaNo on the site itself, companies who are partnered with NaNo give you coupons for different things - half off downloadable writing products, discounts on self-published sites, etc. After NaNo, whatever you do to your story is up to you :)
What happens after NaNo depends on what you want to happen. If you win, then you get these neat little badges to brag with for a year. There are also companies who will offer you free copies of your books if you pay the shipping price for them. I believe they offer you two copies of it.
Other people just throw out their story altogether or they edit it and post it online. Really, there's nothing "official" after NaNo. Just what the individual decides to do with themselves and the novel they wrote. ^.^