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