Hi Alban, you can indeed 'book' a teacher who you have to pay for, and that is how italki makes money. However, you can also just find people who are just willing to teach you English or who want to make a language exchange (you teach teach them Portuguese, they teach you English). In the informal language exchanges it is not necessary to have any teaching experience or the like ;-) I, for example, am interested in keeping up my Brazilian Portuguese (even though I focus on European Portugues at the moment) and teach English. :)