I don't think Skype needs a primer. It is very simple. The explanations on the Skype website are simple and clear, hard as that is to believe.
I tried it myself, before I swiched to Vonage. Skype is like using a prepaid telephone card, while Vonage has the traditional telephone company services, and a monthly fee.
The charges for Skypeout, which is the service for calling any landline telephone, ran me about $.04 per minute, pre-paid. The service I buy from Vonage is $18.50 per month, with tax.
Both are VOIP.
Had a good experience using SKYPE to speak to someone in a South American backwater -- both of us had it installed on our computers and the sound quality was quite good.
Trying to add video to the call r e a l l y slowed things down, tho.