First, download the compiler and components.
Next, add Swift to your path. On macOS, the default location for the downloadable toolchain is /Library/Developer/Toolchains. Run the following command in Terminal:
export PATH=/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin:"${PATH}"
On Linux, you will need to install clang:
$ sudo apt-get install clang
If you installed the Swift toolchain to a directory other than the system root, you will need to run the following command, using the actual path of your Swift installation:
$ export PATH=/path/to/Swift/usr/bin:"${PATH}"
You can verify you have the current version of Swift by running this command:
$ swift --version