'미국에 갔다가 오다' meaning? I don't understand the meaning of the phrase above '갔다가 오다' =???

What is the difference between '공부하다' and '배우다'? In which cases to use each word above. Thanks.

Active Verb + (느)냐고 하다. (Indirect speech) (Someone asks if/whether...) Which conjugation below is right? * 전화번호가 생각나냐고 해요. He asks if you remember the phone number. * 전화번호가 생각나느냐고 해요. Thank you. 감사합니다. ^__^

-고요? What does it mean? Help me to translate this sentence: 치마 입고 가려고요? And explain me the meaning of '-고요'. How to use it? 고맙습니다. ^^

irregular verbs (-ㄹ다 and -ㄷ다)? I am confused about these verbs: 멀다 (far) & 듣다 (to hear, listen) • 멀다: 멀면; 멀수록 • 듣다: 들으면; 들을수록 Is the conjugation here correct??? 감사합니다.

I'm not sure how to translate this sentence "그만 출발합시다." Does it mean 'Stop leave.' or 'Let's start The pattern: 그만 + Verb. 감사합니다.I mean 'Let's start to leave' or 'Stop leave'.

The verb '수줍다' (to be shy) I need your help!!! It's correct when we say '수줍은 미소'. But why not '수주운 미소'??? I mean, the verb with 'ㅂ다' like 귀엽다 should be changed '귀여운 척하지마' for example.

I got confused: 울면 안 돼; or 우면 ??? (the verb 울다)

What's the difference between '여기에' and '여기서'? Thanks.