Yeah, took me a while to figure this out too...
It’s actually quite simple, when you’re typing I sing the folio keyboard - in a program, or a text field, or the web-address bar in safari (anywhere where you type basically) - you need to press and hold the icon in the bottom right corner of the screen that looks like a down arrow. Then the on screen keyboard will pop up and you can press the key next to the space bar that looks like a microphone (make sure you have dictation enabled in settings, otherwise this won’t show.)