input file structure in deepsd_data_prep notebook

Hi everyone. I have a question about the input file used in the deepsd_data_prep notebook, 
"ds =xr.open_dataset("./e5.oper.invariant.128_129_z.ll025sc.1979010100_1979010100.nc")". So, my question is what is this file, and how can i know the structure of it? is there any place which I can download it and extract it?

Thank you very much.