Tableau Basics

Why is my Tableau workspace different from the one in demonstration lecture yet we pull data from the same source? The Dimensions and Measures labels in the lecture do not Show in My Tableau. What appears is a tittle called Table in Bold. Second The generated field called Number of Records in the lecture slide does not appear in my tableau. What is there is Data(count) which I cannot use to calculate Revenue because it returns an error in calculation. The Error is cannot mix aggregate and non aggregate arguments with this function. I am stuck at that point Thanks K.C