Recording a professional soundtrack with impeccable vocal quality and the right audio perspective for each take is a complex process. You must select a mic with the right pickup pattern, position it correctly for a good recording (while hiding it or keeping it out of frame), avoid interference and distortion, and make sure sound levels don't peak over 0 dB.
But it's well worth the trouble to get it right. To an audience, one of the most noticeable differences between an amateurish home video and a professional presentation will be the quality of the soundtrack.
A good soundtrack won't necessarily make your movie, but a bad one will surely ruin it.