Media (music, films etc.) is not available from iTunes in Croatia (presumably because not enough rights-holders haven't yet granted Apple licenses to sell their content there ; or potentially it might be due to your country's laws), so the iTunes U screen is all that you will see in the iTunes Store app - as we are fellow users (these are user-to-user forums) we won't know if/when Apple might open an iTunes store there until if/when they announce something.
You can browse other country's stores, but you can't buy or download anything from them unless you are physically in that country (and have a billing address in that country on your account) - you have to be in a country to use its store.