Here are some websites that I have found helpful and that each take a pretty different point of view.
The most important thing I can say, from my Support Pup Cooper perspective, is that there is no one way to pup. There are pups who will tell you one way to do it and there are others who will tell you many other alternatives. The key is to find your way to pup that makes you happy, wag, and feel most comfortable as a pup. For some pups, it is a purely social thing - a way to meet people, socialize, hangout, engage with others. For other pups it is purely sexual and part of BDSM-type play. And for other pups it is a blend of both. If someone tells you it has to be a certain way, proceed with caution; it may be the case that for them it has to be a certain way and therefore they want you to engage with them in that way. That's fine, but if it is not something you are comfortable with, keep looking for pups or handlers who want to do it the way you do - you will be likely to find it out there!
There are probably more websites out there than I have listed here, so if you find any you think I should add to the list, please let me know by sending me an email using the Contact link at the bottom of this website.
Puppy Play Info. was created by a group of volunteers called Nerdy Doggo, run by a pup named Tycho Aurora. In August 2019, they decided to stop creating new posts or building the site anymore. The site is still available as an archive and has tons of great posts about a wide range of topics in the puppy and pet play world.
SIRIUS PUP is a website run by Jyan Craig and his pack of pups. The website has a lot of information about pup play. One of the things that makes this site unique is that it has a puppy training component with modules about finding and accessing your puppy self. It has how-to pages, quizzes, and a whole lot about protocol. It also has a section that is pretty cool about puppy play around the world and what some of the cultures are in different countries or regions.