ilikesomuch asked: related? then why are they using different words and letters to say same things? (like "kot" "mačka" "kaķis" or "кошка" for cat?) you mean the grammar is the same?

They aren’t the same, they’re related. This isn’t really the place, and I am not a professional linguist (nor do I play one on the internet), but I refer you (and anyone else who’s interested) to the Wikipedia page on the Slavic language family, which is a good place to start.