Maggie - to find the microphone, from the W10 start panel, click on the "Settings" icon (the little cogwheel symbol down the extreme left hand side, immediately above the Power on/off icon.
The settings screen will open with a search bar at the top. Type "microphone" into the search bar and hit return. You will be offered a list of options.
Click on "Set up a microphone" and you will be taken to a page headed "Speech".
Scroll your way down the choices there - choose your language, choose the default voice for apps (I liked George but slowed down just a little!), and eventually you get to Set up a Microphone.
Just follow the instructions. The system asks you to read a sentence aloud from the screen to ensure it can hear you clearly. Keep working your way through the screens until you're done.
And the best of luck!