Let's make a simple sentence in Korean.
As you know Korean has 2 ways of sentence formal and informal
We use informal way among friends, family and use formal way to not so close people, group of younger people or boss, teacher...
Anyway you just have to know how we can make formal sentence with informal sentence.
Let's see~
밥 먹었어 -> 밥 먹었어요 / 책 읽었어 -> 책 읽었어요
Do you find a difference of them? yeah, we put '~요' end of word.
Usually we can make formal way with this rule but you have to know 밥 먹었다 -> 밥 먹었다요(x)
We use more ~다 in the writing not speaking ~다 changes as 습니다 in this case
1. ~어 + 요 / ~나? -> 나요? / ~니? -> ~나요?
2. ~다 + 습니다 / + 습니까?