When you're signed in to your Office 365 account, turn on your microphone, go to Home - Dictate in Word, Outlook, PowerPoint, or OneNote for Windows 10, wait for the icon to turn red, and start talking!  

For more tips like this, check out the working remotely playlist at www.youtube.com/FoetronAcademy . Also, if you need any further assistance then you can raise a support ticket and get it addressed.