Hi Viviana

Just to clarify, I'm not hosting this class - this is one I learned of and posted here because I thought others might be interested.
Most of these teleclasses are set up on a local United States number. You register for free and they email you the number you will dial to access the call and tell you what time and date, etc.
When it's time for the teleclass, you just dial the number and follow the instructions when you get through. Most teleclasses are set up with buttons for 'mute' etc. and then you listen to the host's instructions, information, etc.
There is usually a period of info at the start and a Q & A at the end. This one sounds like it has some actual exercises you will do on the line with other callers and the host to help you get started in improving the confidence in your voice.
I hope that helps explain!

If you're worried about the cost of the call, Skype is a great way to access these calls internationally for a small amount of money. When we were abroad I was on Skype for hours at a time some nights and it would cost like $2.00 U.S. (not bad!)
Hope that helps!