You do have to have a mic connected to your computer, of course, but laptops have one built in and so do a lot of monitors.
It works remarkably well, and the speech recognition is very, very good. No training is needed. Along with dictating text, you can also say the names of punctuation marks to add them, and say "new line" or "new paragraph." It doesn't have a command language, though, so you can't use other functions in Word, like italicizing, as far as I can determine.
The only drawback of it is that all dictation goes to the cloud where the speech recognition stuff is located. It's fast, but not as fast as I can type.
According to Microsoft, when you turn the feature off, all of the cloud storage is deleted.
To use it, just click the microphone at the far right of the ribbon at the top of the Word window.
I don't use it on a normal basis, but I have used it for note-taking a few times, It can be useful for that. For example, if I'm reading a technical book, I can open Word, start the microphone and just speak the notes I want to record.
If you use Google Docs, you can dictate into that application, as well. I haven't tried that, because I don't use Google Docs. Before long, I'm sure, you'll be able to use it anywhere in Chrome, like on DU, to dictate text. Maybe you already can. I don't know. All speech recognition is done in the cloud, so your words are sent off into space somewhere.
There's a free Chrome extension called VoiceIn that lets you dictate text anywhere text can be input from Chrome. Like on DU, for example. You just right click in the text entry area or field, and click Record in the drop down menu. Then you speak. You can say punctuation words to punctuate and say new line or new paragraph. I haven't tried this yet, but will.