"go'i" means "yes, I agree with you". Sometimes in English, the word 'yes' is used to mean other things. For example, you might say "Yes" (or "OK" or "uh-huh") to tell someone that you heard what they are saying. In Lojban you do not say "go'i" for this; instead you say "je'e" (sounds like "zhehheh"). This is part of the idea of lojban: to make words easier to understand by making sure that one word can only mean one thing.