"오후에 집에 가요."
Translation:Let's go home in the afternoon.
That is the formal "let's" and this is the less formal but still polite "let's"
From my understanding 가 is to "go" and using ㅂ시다 or 요 is depending on how formal you are speaking. The word "Let's" is omitted, it is implied when the speaker puts it into action, like "하지 or 하다" in this instance 가요 let's go.
Right. The original form of the verb is 가다, and the usage varies on which 'verb endings' you use in a sentence. I personally like to compare it with conjugations in several European languages.