For regular students the application process is described on the page below.
As you can see there, before applying for your student visa, you must be pre-enrolled at Iuav.
For all international students it is true that the Italian diplomatic office in your country of residence may also ask for additional documents, such as an acceptance letter or a study plan. We will provide them upon request, but normally a Universitaly portal request is enough.
Ensure you begin the preparations well in advance of your intended start date. In some countries Italian immigration procedures take a lot of time and in some of them you need to apply not too soon before departure, so it's better to get informed about your local situation by contacting an Italian diplomatic office in your country of residence.