Flutter SDK

You have to download and setup flutter from flutter.dev. You can follow documentation with your own device.

Windows: https://docs.flutter.dev/get-started/install/windows

Mac: https://docs.flutter.dev/get-started/install/macos

Linux: https://docs.flutter.dev/get-started/install/linux

flutter doctor

Then check that every setup is okay. If not then check documentation again and set up flutter sdk properly.