right click on the sound icon in the taskbar (bottom right of the screen in win 7/8/10) and click on playback devices. Select the recording tab, then select the Webcam and set it as the default recording device. Done.
As far as getting a soundcard goes, it's really not necessary unless you are using some very high end devices like $300 headphones or $1000 speakers etc. At that point it makes more sense to use a USB external sound solution anyways, as the isolation of being outside the case makes for better sound for some reason (interference and such, they say). When you get the headset, you just plug it into the green and pink jacks at the back of your case and away you go. If you already have speakers plugged in back there, you'll have to use the front panel jacks on your case. Almost every modern case has headphone and mic jacks on the front. Make sure that your front panel audio lead is connected properly to your motherboard from your case's front panel. If you didn't build your computer, it's highly unlikely that whoever built it forgot to hook this up so you're good to go.
Also I say this to help not to be a d-bag. If you DID build your PC and it was your first time, make sure you have the HD Audio/HDA lead hooked up from your front panel and NOT the AC97 lead.
Here's a helpful image
With most motherboard audio solutions you will need to go back into playback devices like I just explained and you will have to select either the rear or front outputs from your integrated sound. So if you want to use the headset, you select front panel as the default playback device. Speakers? Select the rear outputs.
Sorry for the rant. Cheers.