IMPORTANT - READ THIS

How to download a VMU savegame?

SAVE THE VMI FILE AND THE VMS FILE TO THE SAME DIRECTORY WITHOUT RENAMING THEM ! YOU NEED THE VMI FILE AND THE VMS FILE, BOTH ARE NECESSARY AND CAN'T BE USED SEPARATELY ! The VMI file only contains file's info (size, name, etc...), as for the VMS file it contains savegame's data
or else, you can save only the DCI file which contains both info and data in one file in the format used by Nexus memory cards
if you want to rename the savegame you can edit the name in the "Filename" field before downloading the file

How to use a VMU savegame with a real Dreamcast?

download Dream Explorer
start Dream Explorer, select the VMI file or the DCI file in the list and upload the savgegame to one of your VMUs

How to use a VMU savegame with a Dreamcast emulator?

download VMU Explorer
download the batch file for Chankast or NullDC
put VMU Explorer and the batch file in the emulator's directory, then double click the batch
choose a VMU and select the VMI file or the DCI file thanks to the "File > Import file..." menu
save changes to the VMU thanks to the "File > Save VM" menu