The following example changes the format of cells A1:D5 to bold.
Workbook.Sheets[1].RCRange[1, 1, 5, 4].Font.Bold := true;
The following example changes the value of cell B3 to 100.
Workbook.Sheets[1].RCRange[3, 2, 3, 2].Value := 100;
The following example merges the cells B2:C5.
Workbook.Sheets[1].RCRange[2, 2, 5, 3].Merge(False);