Some ways to download it include from

https://swift.org/getting-started/ -> The Swift Website (Tutorial there)
https://apps.apple.com/us/app/swift-playgrounds/id908519492 -> Swift Playgrounds
https://apps.apple.com/sg/app/xcode/id497799835?mt=12 -> Xcode

Note that for Swift Playgrounds, it can only be downloaded on ipads and macs
For Xcode, if your mac is after the Big Sur update (11.0), xcode is free