Arwa 님 ^^
To make it really short,
입은 - wearing (being wearing)
입는 - that wears (does wear generally)
검정 바지를 입은 남자가 웃고 있어요.
The guy who is wearing black pants is laughing.
저는 검정 바지를 입는 남자가 좋아요.
I like the kind of a guy who wears black pants.
Hope it helps :-)