Excel normally has colomn labels (i.e. A, B, C, . . .) , but I see colmn
labels that are the same as the row labels (i.e. 1,2,3, . . .). How can I
change it back to ABC?

NOTE:
I want to write a formula (i.e. 2C=1A+1B).
Exsiting: is something strange (i.e. =RC[-4]+RC[-3]) that I don't understand.