When you start a new page, you'll see a dropdown menu with the option "select boilerplate". Just pick the boilerplate for the page you want to make and click "Load", and all the appropriate categories and any required templates will be added for you.
Some work and trope pages have the same type of subpages, so something like "Headscratchers" would be for tropes, and "Headscratchers Work" would be a headscratchers subpage for a work.
Let me know if you have any questions, and I hope you have fun editing here. :)