1st, 입고 가다 is consist of two verb. 입+ -고 and 가다 Verb is conjugated you know. So 입다 + -고 : -고 is 보조사 which is kinda-suffix(postposition) that contains the verb’s meaning or restricts it or just simply connecting. 가다 means go. So in this sentence there are two verbs. In Korean grammar, it called 본용언 + 본용언 structure, or 본용언 + 보조 용언 structure. ( i don’t know this words in English, sorry....) +) -고 is postposition which is hardest part of Korean grammar when English speaker learning Korean. Because its concept, postposition is not exist in English grammar. Anyway, important point is postposition, but it is difficult to tell you right now. If my description is terrible, I’m sorry about it. Have a nice day!