How can I do a statistical ysis using these data?

I have 3 variables that can affect the outcome of a process. Let's call them A, B and C. I can't alter the variables, all I can do is look at past data (A B C and the outcome). How can I use excel, or what is the best way, to yze this data? I want to see in the past which variable affected the outcome the most, or if it was a certain combination. I have a basic understanding of statistics, and am willing to research other methods. Just not really sure where to start. Thanks in advance.