"Dad lends me his credit card."
Translation:아빠가 신용카드를 빌려주세요.
shouldn't the sentence in english say: Dad, please lend me your credit card?
It's not. See the 가? You don't use that when talking to other person directly. Present tense, present interrogative, and imperative have the same conjugation in casual form, the only difference is the intonation. 해요. 해요?. 해요!
Adding 세 originates from adding 시다 to make a verb more polite. Originally it was 하시어, then 하셔, and now it changed to 하세 to ease the pronunciation. Without 시, it would be 빌려줘요.
The sentence could've not use 요 at all, instead using written and formal form, 빌려주신다 and 빌려주십니다.
It could be a request, but it could also be a statement. Or a question: Does dad lend me his credit card? In the formality level marked with -요 at the end, all of these look the same so you have to rely on context (and intonation) to know which is meant.