~ㄴ/는/ㄹ 것 같다 (geot gatta) means something you think/it appears/it seems to be ~. So for example, 쉬운 것 같아 means something appears easy, or 예쁜 것 같아 means something appears pretty or "I think it's pretty." 냐 (nya) is a question ending that I believe (not 100% certain on this) began as a form of -아니야? that kind of just faded to -냐? over time. Either way, is is merely used to mark the sentence as a question, though it can come off as kind of blunt depending on the context and who you are speaking to. However, you don't always have to use -냐 to ask basic questions: you might also use -니 or no ending at all. "미쳤어?" and "미쳤니? are also valid ways of saying it.