The following example changes the format of cells A1:D5 to bold

Workbook.Sheets[1].RCRange[1, 1, 5, 4].Font.Bold := true;

Workbook.Sheets[1].RCRange[3, 2, 3, 2].Value := 100;

Workbook.Sheets[1].RCRange[2, 2, 5, 3].Merge(False);