Windows 10 includes a built-in Voice Recorder app, which can be found in the Start Menu.
When first opening the app, it will ask to use your microphone. Answer 'yes'.
Next, you will see this screen. It looks a bit vague, but all you need to do to start recording is to press the big button right in the centre of the window. It will begin to record straight away, so make sure you're ready.
If you have a headset plugged in, it will automatically use that to record; otherwise, it will use the microphone built into your laptop. A headset is recommended as the end result will be much clearer.
When you've finished recording, click the stop button. You'll then be able to play your recordings back.
To find your recording on your computer (for example, to send to others), right-click on the recording on the left-hand side, and click Open File Location.
By default, recordings are saved in your Documents, under a folder called Sound Recordings. This also means they will automatically sync to OneDrive.