Use dictation to enter text

With keyboard dictation, you can dictate text anywhere you can type it. A feedback window gauges your speaking volume and provides basic dictation controls.

Place the insertion point where you want to begin dictating or select the text you want to replace. 
Choose Edit > Start Dictation from the Edit menu at the top of your screen.
If you haven’t used dictation before, follow the guided setup instructions that appear.

Tip: When dictation is set up, you can also press the Function Fn key on your keyboard twice to start dictation.
When the microphone appears, begin speaking.
To add punctuation, speak its name (for example, comma or apostrophe).
Click Done below the microphone when you’re finished.

To learn more about dictation, go to Mac Help. Click the desktop to switch to the Finder, choose Help > Mac Help (from the Help menu at the top of your screen), then search for "dictation".