Windows
SwiftForth for Windows is supplied as a Windows installer. Just run it and follow the prompts.
macOS
SwiftForth for macOS is supplied as an Apple installer package. After you download it, run the .pkg installer. It will install in your Applications folder as /Applications/ForthInc/SwiftForth. It will also add symlinks in /usr/local/bin so you can run sf and sfk from any Terminal session.
Linux
SwiftForth for Linux is supplied as a tarball. After you download it, cd to the location in which you want it expanded and unpack the tarball:
cd <new SwifForth parent directory>
tar -xzf <path to downloaded tarball>
Then cd to the new SwiftForth directory and run the install.sh script. It will install sf and sfk symlinks from /usr/local/bin back to the SwiftForth/bin/linux. It will also remove any ~/bin/sf* symlinks (so restore those later if needed).
cd SwiftForth
./install.sh
When you run sf from the command line, you should see this:
~$ sf
SwiftForth x64-<os> 4.x.x <date>