yamlfmt can collect paths in two modes: Standard, or Doublestar.
In standard path mode, you can specify a file or directory path directly. If specifying a file, it will simply include the file. If specifying a directory, it will include every file with the correct extension (as specified in extensions, default is yml and yaml).
In Doublestar mode, paths are specified using the format explained in the doublestar package. It is almost identical to bash and git's style of glob pattern specification.
In both modes, yamlfmt will allow you to configure include and exclude paths. These can be paths to files in Standard or Doublestar modes, paths to directories in Standard mode, and valid doublestar patterns in Doublestar mode. These paths should be specified relative to the working directory of yamlfmt. They will work as absolute paths if both the includes and excludes are specified as absolute paths or if both are relative paths, however it will not work as expected if they are mixed together. It usually easier to reason about includes and excludes when always specifying both as relative paths from the directory yamlfmt is going to be run in.