Alright so this guide is going to be real basic, I'm just going to explain the history behind this forum, what you can expect to find from it, and some basic policy involving it.
Pokémon & Challenge Discussion (henceforth labeled PCD) as a forum evolved from two separate forums back on or previous site, Zetaboards and then Tapatalk - unsurprisingly named Pokémon and Challenge Discussion. In streamlining and consolidating forums with the move, we were looking to find forums that had a lot in common that could be meshed together, bringing us to PCD. Since they shared a broadly similar scope (Pokémon and discussion of the Nuzlocke challenge, respectively) it seemed a natural fit.
So PCD is for discussion of the Pokémon series in all forms (main games, side games, anime/manga, movies, what have you) along with discussion of the Nuzlocke challenge and different aspects of it, along with resources and information to help make the Nuzlocke challenge easier. Most of the threads you see will center around some of these things mentioned, though they may also simply involve Pokémon generally.
Here is a quick overview of the prefixes found in this forum, first labeling the Pokemon-specific ones and then the ones that it shares with Entertainment.
Nuzlocke is for any threads related directly to Nuzlocke content - so if it applies to non-Nuzlocke things, too, or isn't primarily aimed at them, probably best to leave them off.
Ruleset is for threads about rulesets, specifically - ones of your design or ones you particularly like. This is often paired with the Nuzlocke prefix, but it doesn't have to be if you have a ruleset idea that's not a Nuzlocke one.
Competitive is for anything involving Competitive Pokémon battling and things in that sphere.
Advice is for threads where you can ask for advice from other people - keep in mind it's usually better to make a general advice thread for specific kinds of problems than to make a one-use thread for the single issue you're having! The thread will have more longevity then.
General is for threads that don't really fit into any of these boxes. It's a fairly optional prefix, but nice if your thread doesn't really seem to go anywhere else.
Now for the entertainment media prefixes. Firstly, Video Games refers primarily to Pokémon-related content that is not Nuzlocke; items prefixed with Nuzlocke can be assumed to involve video games, and as such it's unnecessary.
Anime/Manga is, as the name implies, for discussions about Pokémon anime and manga specifically. Simple.
Movies is for discussion of the different Pokémon movies.
Now for a couple of important policy details regarding PCD, things to keep in mind while you're browsing here. The first thing to note, something new for this board, is that forum games about Pokémon (such as Fix a Move or Design a Mega) are now going to be held in the Festival Plaza subforum.
We felt that those games had more in common with Festival Plaza, and we didn't want them to be competing with a different type of media for attention. If we see these games in PCD, we'll simply move them. Easy enough.
The other thing is about spoilers. People enjoy performing blind playthroughs of Pokémon games for many reasons, and one of them that is core to our values is to increase the challenge of the games. So, to that end, we take unchecked spoilers about new main series Pokémon games very seriously. It is typical policy at this point to stage an embargo on unmarked new game spoilers until one month after the game's release, to give people time to play through them. Even after this point, we ask that people be respectful and considerate especially about climactic later game information. You may be warned for repeatedly leaving unmarked spoilers outside of threads for discussing these spoilers, so be aware of where and how you are discussing new games, and make sure to mark spoilers in otherwise spoiler-free threads.
Well, I think that's everything, so have a fun time in the combination Pokémon and Challenge Discussion!