Go to the Skype website and create a free Skype account. You will then need to install Skype on your pc or mobile device. You will be given a Skype id, you will need to share this with your teachers / language partners.

Adding to the Saqib's answer, To do a class with two or more people in the same chat, you just have tu invite to a person in a chat, so then, in the same chatroom just keep adding persons in the option above the principal screen, and you can speak at the same time with 1 or more persons.