When it comes to the pronunciations, you do not need to know the meanings!
발음 연습을 할 때 의미까지는 몰라도 괜찮아요!
Palatalization of ㄷ & ㅌ
When ㄷ or ㅌ occurs before the vowel ㅣ, the pronunciation becomes 'palatalized'. Basically, tgus means that ㄷ and ㅌ change to ㅈ and ㅊ respectively. Note however, that this change only occurs when the ㄷ or ㅌ is at the end of a word or stem and the ㅣ is part of a suffix, verb ending, particle or the copula. It does not occur elsewhere.
참고 Jaehoon Yeon and Lucien Brown(2011), Korean: A comprehensive Grammar, 30-31.