Simplest: get a field recorder like a Zoom H5 and use the built in microphones. Use the SD card to transfer the audio files to your computer and do what you want with them
Next: get a condenser mic and plug it into the Zoom for better sound. Process the audio files on your computer with audio software like Audacity (free) or Reaper ($US60) to add a bit of reverb and edit out the bad bits. Render down to MP3 or other files.
Third level: get a USB audio interface for your computer and whatever audio software works with it. This will let you make audio files directly in the program instead of importing them from a separate device. You can also do multitrack recordings if you wish. But you gain the hassles of temperamental interfaces, their drivers, software compatibility issues and also the fan noise of the computer intruding on your recordings.