What's the difference between ` Swift module` and ` Swift Package Manager module`?

Question

When I use the sourcekitten tool in macos terminal:

% sourcekitten doc -h

OVERVIEW: Print Swift or Objective-C docs as JSON

USAGE: sourcekitten doc [--single-file] [--module-name <module-name>] [--spm] [--objc] [<arguments> ...]

ARGUMENTS:
  <arguments>             Arguments passed to `xcodebuild` or `swift build`

OPTIONS:
  --single-file           Only document one file
  --module-name <module-name>
                          Name of Swift module to document (can't be used with `--single-file`)
  --spm                   Document a Swift Package Manager module
  --objc                  Document Objective-C headers instead of Swift code
  --version               Show the version.
  -h, --help              Show help information.

I have several questions about it:

1. what's the difference between Swift module and Swift Package Manager module?

2. in terminal, how to location the Swift module and Swift Package Manager module? where to find them?