A Folder value is a path to a folder, directory, or zip archive. It's the required input to the Workdir container — see Workdir Type for how that container turns a Folder path into an active working directory — and it's also what Folder Junction picks between when choosing one of two possible folders coming from different execution pipelines.
The folder editor presents a browser for selecting the target folder, directory, or zip archive, or typing its path directly.
A Folder constant is written in EGO Script the same way as a String literal, enclosed in double quotes:
"c:/data/"
See Type System for the complete conversion reference across all types.