Siri isn't the same as Dictation, but you can ask Siri to compose short messages, such as email and text messages. In macOS Sierra, you can ask Siri to “turn on Dictation” for you. Choose your preferred microphone from the pop-up menu below the microphone icon.Choose the keyboard shortcut you will use to start dictating.Some languages, such as English, have multiple dialects. Choose whether to use Enhanced Dictation, which lets you use dictation when you're not connected to the Internet.
Turn on Dictation and choose from these Dictation options:
Choose Apple menu () > System Preferences, click Keyboard, then click Dictation.
