Hi Manolo, this is the same as in Spanish. When you say "voy a practicar...", in English you say "I am going to practice the piano." or "We are going to Brazil for a holiday."(you have already made plans). If you have just made a decision now, eg, "No tenemos nada de huevos? Iré a la tienda..." "We have no eggs? I will go to the store and buy some." or "I think I will have some lunch, I am hungry." Compare these two answers: Do you want to come to a party tonight? 1. Sorry, I'm going to a concert. I already have some tickets. (I am going...) 2. I'll come! I don't have any plans. (I will come!) I hope this is helpful!