Okay kiddo, let me explain to you what South Slavic languages are. Imagine you have a friend who speaks a different language than you do. Maybe they speak Spanish, French or Chinese. Now, there are a group of languages called South Slavic languages that are spoken in parts of Europe, mostly in the Balkans.
These languages include Serbian, Croatian, Bosnian, Montenegrin, Macedonian, and Slovenian. They are all part of the Slavic language family which includes other languages like Russian, Polish, and Czech. These languages are similar because they all come from the same roots, kind of like how you and your friend might also have some things in common despite speaking different languages.
Each of these South Slavic languages has its own unique features, like different words, grammar rules, and pronunciation. However, because they are so similar, people who speak one of these languages may be able to understand someone who speaks another South Slavic language even if they don't speak it themselves.
For example, imagine you speak Croatian and your friend speaks Serbian. Although there might be some differences in the words you use or how you say them, you could probably understand most of what your friend is saying. This is because these languages have a lot of similarities and share a lot of vocabulary.
So, that's basically what South Slavic languages are - a group of languages spoken in parts of Europe that share a common history and are similar to each other.