"So far" means "until now". You use "so far" when you are comparing what has already happened with what is going to or might happen. For example:
We've made over fifteen million dollars so far this year.
This means that they have made fifteen million dollars already this year, but they will make more before the end of the year.
I started playing the guitar last year. I haven't performed publicly so far, but I think I'll be ready soon.
This means that the speaker has never performed guitar publicly yet, but might perform in the future.