Right, then let’s do this. I will keep this focused on D&D, as that is what I know, but take what you can from this. I will start with some resources and then I’ll kind of lay out how I went about it. This may be quite long. You have been warned.
First off, Matt Colville’s youtube channel is just absolute gold should you want to get into worldbuilding with the express purpose of playing role-playing games. He covers a lot of ground talking about everything from implicit assumptions within your worldbuilding to straight-up how to make an interesting NPC. The channel is definitely more about how to DM, but nevertheless, some of it applies and he’s just good at making engaging videos. Highly recommended!
Another channel that I like is WebDM. Again, very much focused on D&D and DMing, but they branch out to other systems and talk a lot about common themes within fantasy and D&D and how to make interesting twists on them. They are more useful for inspiration for me, as they have a very conversational style that I like.
From these two channels, should you enjoy them, I’m sure you will find many similar ones, so I’ll stop here. There is also this collection of links that I have used many times when I was stuck or didn’t know what to work on. The last thing you will need is a way of organising your information. I use a patented method of different notes in different media, all scattered so that I myself never know what is going on at any one point in time. But I’d recommend notebook.ai, one note or even just google docs.
Now none of this really tells you where to start, which is probably the most important question. So I will try to show you a couple of approaches that I used and how it panned out for me.
In my opinion, you can do one of two things. You can start big, or start small. To me, when building fantasy worlds, this means asking myself: do I draw a map or do I construct a town? (Spoiler: I did a combination of both and cannot recommend that. Building cities is hard.) Let’s look at an example!
This is my world. The map is iteration 3, I think, but the original looks very similar. I did not do any planning, I just drew something that looked nice, made some modifications and boom, there you go. My players, in game, have seen about 0.001% of the map, I maybe know what 0.01% of it really is. So one thing I have learned is that it’s good to have enough space. If you look at the map, some parts are not shown. I do not know what lies beyond the map, and that has been good as well, since it gives me room to expand. Most importantly, all of these aspects enable me to have player characters be from anywhere and, should they want to, give them a place that they can build themselves!
Once you have a map, draw some mountains and rivers. You can read up on how mountains come about, or you could just place them wherever you like! Maybe mountains grow where great sorcerers die or maybe they were placed by sentient cakes. It’s your world, go nuts! With mountains and rivers, you have natural borders. Islands function in a similar way. Then you can think about civilizations. Where would people go in your world?
// Quick sidebar: Note how many assumptions I have already made. There are continents, mountains, the ground is made of earth, our natural processes seem to apply, etc. I find thinking about these things before worldbuilding tedious, and since my world needed to be recognisably fantasy medieval europe, I had little room for creativity in that regard anyway. I like making these decisions as they arise.
Let’s take a break from the big picture. Starting small is far less intimidating, but you make slower progress. If you know what time period you’re in and what technology your inhabitants have access to, constructing a town is straightforward. You can go with your gut as to what buildings are in a small medieval town or you can read up on it. (This will be the start of your highly specific google searches.) Again, we’re making a ton of assumptions, but we want to play D&D! Ideally soon! Once you know what buildings or what professions are a part of your town, you will have the thankless job of creating people that are interesting enough that your players will engage with them. Maybe this means that there is a priest of a god in the town! Are there gods in your world? Do your clerics worship sentient cakes? Why not? Maybe one of your players is also a cleric, but he worships the god of cookies, and so you have conflict. What are the tenets of the religion of Uhrgarbl, the great chocolate chip?
I think you can see that, essentially, worldbuilding just is asking a series of questions within constraints that generate more questions. To me, having a goal (like engaging my players) is paramount to getting anything done. I wouldn’t know how to construct something as a context for music, but I’m interested to see what everyone else says! Should anyone want to know more or more specific things, feel free to ask.