Skype is an excellent product but if its any good to you depends on what you need in communications. It requires you have at least some form of speakers and microphone [or headset] on your computer.
Its free to subscribe and free for Video, speech and texting between other people on Skype anywhere in the world.
If you place some credit on it as has been said you can then also use it to make low cost calls to land lines throughout the world. This feature is called "Skype-out"
So if your not buying that feature in your landline rental that can represent a huge cost saving.
In recent times it has become a FREE feature on 3Mobile. This allows you to use the speech and texting feature free to any Skype user, but a huge plus for some is that it also allows you free access to your "Skpeout" account to foreign landlines. So very cheap use of your mobile for international calling.
A feature Skype has is that it shows you who of your "contacts" are actually sat on their computers. So you don't fruitlessly call somebody who is not immediately available. "Contacts" are those with whom you have agreed to be included in your personal list of Skype acquaintances.
As I said in its basic Skype to Skype form its free so exploring it cost you nothing, but for others to "see" video of you then you need to buy a webcam. Almost all webcams include a microphone as well.