Install the SpeechNotes app from the Web Store. Once installed, click on the App Launcher and then on the SpeechNotes app. Alternately, you could just bookmark and visit. Another option is to visit https://speechnotes.co/. Follow the site instructions to dictate and copy your text.
Another option is to enable Voice Typing in Google Docs. In Google Docs, click on Tools>Voice Typing. It will open a microphone. When you are ready to speak, click the microphone. When you are done, click the microphone again.