$ mkdir TodoKit
$ cd TodoKit
$ swift package init

// Depending on a branch (master in this case):
.package(
    url: "https://github.com/johnsundell/files.git",
    .branch("master")
)

// Depending on an exact commit:
.package(
    url: "https://github.com/johnsundell/files.git",
    .revision("0e0c6aca147add5d5750ecb7810837ef4fd10fc2")
)

.package(
    url: "https://github.com/johnsundell/files.git",
    .exact("4.0.0")
)

let package = Package(
    ...
    dependencies: [
        .package(
            url: "https://github.com/johnsundell/files.git",
            .exact("4.0.0")
        ),
        // Using 'path', we can depend on a local package that's
        // located at a given path relative to our package's folder:
        .package(path: "../CalendarKit")
    ],
    targets: [
        .target(
            name: "TodoKit",
            dependencies: ["Files", "CalendarKit"]
        ),
        .testTarget(
            name: "TodoKitTests",
            dependencies: ["TodoKit"]
        )
    ]
)

// swift-tools-version:5.1

import PackageDescription

let package = Package(
    name: "TodoSwiftUIComponents",
    platforms: [.iOS(.v13)],
    ...
)