If you want the best experience learning Swift, using Xcode on macOS is the way to go. Xcode is Apple's official IDE, and it lets you build iOS apps, test them with the simulator, and build/deploy your project all in one place.
If you don't have a Mac yet, you can start out with an online Swift playground to try the basics — syntax, variables, loops, functions. Once you're ready to move on to an actual app project, you'll need Xcode.
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You'll be able to run Swift code instantly inside Xcode Playground.