All you need to do is plug it into your computer it will walk you through setup is like $19.99 for a year unlimited or $69.99 for 5 years. Will let you pick number or you can transfer your old number to the magicjack. Then every time you plug it in it will display in the upper center part of the magicjack application.
Magicjack changed their price for a year of service, to $29.95, if you buy the 5 year plan its comes out to $19.95 a year, there is a cost to change number too. I use one all the time,