AND(condition1,condition2,...) returns 1 (=TRUE) of all of its arguments are TRUE.
If one of the arguments, either condition1, condition2, etc. is FALSE (=0), the function returns 0 (=FALSE).
If one of the conditions cannot be evaluated (for example because of missing data), the function returns an error.
If GROUP and TREATMENT are variables defined in the spreadsheet then:
AND(GROUP=1,TREATMENT="B") returns 1 (=TRUE) if the case belongs to group 1 and received the treatment coded as "B" in the spreadsheet.