Setting up
You will need to have a microphone that can plug into your computer. The microphone; must have a '3.5mm' plug at the end of the cable, like the picture below.
If the plug at the end of your microphone cord does not look like this then you won't be able to plug it into your computer. If you have the correct plug then you need to plug it into the 'mic-in' of your computer.
The mic input can look very differently depending on the computer you are using. Here is an example of a mic-in (the blue input on the far right) in the image below:
Now you must plug in the mic and place the mic close to your interview subject. You may wish to hold the mic in your hand so that when you ask questions you can turn the mic towards you so it can record what you say clearly. When you have finished talking be sure to point the mic back at the interview subject. Getting this process right is quite a trick. One thing to avoid is bumping the mic or rubbing it while you hold it as this noise will be picked up by the microphone and recorded. Be sure to move the mic steadily and quietly.