When you are saving a .CSV in OpenOffice you need to include some extra information so SellerExpress can import the file correctly. When saving your file select 'Save As' then tick the option "Edit Filter Settings" as shown below,
Once you hit "SAVE" another box will open, on it select your "Field Delimiter" as a comma and the "Text Delimiter" as blank. Once you are done click ok.
You can now go ahead and import your file.