You will understand much only by using standard Croatian, but not everything since there are around 35% literally the same words but the rest can be guessed from context or just learn words. And Croatian has 3 dialects where only one, used as standard due to political reasons in 19th century, has the cousin dialect in Serbia which enables us to understand each other without major problems, the two others spoken in Zagreb/Northern Croatia and one in littoral part have very low mutual intelligibility, lower than Spanish/Portuguese. :) Of course, the answer from a sir from above can confuse you since he lives in Bosnia which is mixture of everything and he can understand much, like my grandparents, who lived in Yugoslavia where everything was trying to be unified but due to many differences throughout 900 years of separable development it didn't succeed. =) Looking forward to our conversations, I will do my best to help you =)

Yes my friend, you will be able to understand all of them. They are 95 % the same. Before the civil war in former Yugoslavia those languages were only the one: Serbo-Croatian. But politics is sometimes more important that all other sciences, this time more than linguistics. Kamenko

Yes, you'll understand those languages. Plus, you'll understand most of Macedonian and at least half of Slovenian.

Serbs from Serbia speak ekavian but Serbs from Bosnia & Herzegovina and Croatia speak ijekavian. About 1/4 of kajkavian Croats are mostly ekavian speaking. Also Croatian majority spoken dialect is ikavian. Ijekavian was originaly spoken only in Dubrovnik-Neretva County and few other cities.