Studio offers many tools to help you develop and publish packs. Studio makes use of Studio Worlds, which are development worlds. It features many useful commands to develop Dimensions.
Studio Worlds are fake worlds, created solely for the purpose of testing and developing. You cannot and should not use these worlds to build in, since they are removed every time the server restarts.
These worlds can be opened with /iris studio open. Make sure to read the command description & parameter options for that command, in /iris studio's command list before opening one. If you are on a local machine, this is also going to open VSCode with the workspace for this dimension. You can also open VSCode without opening a studio world with /iris studio vscode <dimensionName>
The key feature of these worlds is that they hotload. This means that every time you make a change to the pack (found in */plugins/Iris/packs/<yourPackName>), it will apply those changes to all new chunks you generate.
You can find biomes in Iris worlds with /iris studio goto. Note that you can also, to see only the new biome or region you created, enable force and forceRegion (see Dimensions - 5 Elements).
You can view Dimensions' properties with multiple useful GUI-based tools. Note that you will need to run the server on your local machine to see the GUI.
You can get a preview of many elements of the dimension currently loaded in the studio world. Open this preview with /iris studio map. This map shows noise styles for biomes & regions, object density, and multiple other features.
Get a preview of all the basic noise types Iris features with /iris studio noise. You can zoom in and out by scrolling, and drag by holding left mouse button.
You can explore your noise generators */<packName>/generators/ with /iris studio explore <generator>. This allows you to see exactly what you created, making it easier to debug & tweak.
Studio worlds and the other tools Iris features are really powerful tools to create new biomes, dimensions, objects, and much more. The commands displayed here are not all the commands featured. Make sure to, as always, check out the full category of commands: /iris studio.