Function keys are used within specific programs. e.g. in Internet Explorer (and all other popular browsers), F3 brings up the search box (so you can search for text within the page), F5 refreshes the page, F6 highlights the web address (so that can start typing a new one) and F11 toggles full-screen mode on and off.
However when you use a different program, such as Microsoft Word, the function keys perform completely different tasks. So it would be impossible for Dell to tell you what the function keys do (as they don't know which programs you'll be using). You need to google the name of the relevant program, together with the word 'shortcuts', to get a list of what can be done using the Function, Alt and Ctrl keys.
Your loss of sound might be due to a corrupt audio driver. Start by running the hardware test here:
http://www.dell.com/support/home/uk/en/ukbsdt1/product-support/product/xps-m1330/diagnose?rvps=y
Your webcam needs a program to make a call on it. So installing Skype (or any other software that uses a webcam) should see it working for you.