Where exactly to add serialize hook (emberJS)

I have been following the EmberJS tutorial at tutorialspoint.com, and was going through the "routes" section, when I came across this page. It explains how to use dynamic segments in ember. So far I understand the code on how the route.js is updated and how the hbs file is created etc. (that's all pretty straightforward). What I don't understand is the last part where a serialize hook is made. I understand the code, but don't exactly know in which file should I put it? There is no mention of it in the tutorial, and I searched stackoverflow as well but the only answer relevant to this was this where it explains how they work rather than where to add them. Can someone please explain in which file should I add this code? Thanks.