You have to wait for a interview appointment at the US embassy, which may take a few weeks or even months, go in to be interviewed, and then the visa will be mailed within a few days. F-1 visas are almost always valid for 5 years and multiple entries, if you are citizen of a EU country. Your actual length of stay, however, is determined by the end date of your I-20 and/or the duration determined by the immigration officer upon arrival.