This Minecraft tutorial explains how to program a command block to summon a villager to do a custom trade in Minecraft with screenshots and step-by-step.
With Visual Studio Code, sample JSON files, and a wealth of documentation and tutorials, you'll learn how to build your own custom mobs, items, and more in no.
You can create custom gamerules, they're kind of like custom commands. Here is an example of using a gamerule to set your spawn to your current location.