You need "PS2 Classics Placeholder" (by CaptainCPS-X) installed and your ps2 classics in /dev_hdd0/PS2ISO as subfolders. It is also available for download in mM's WEB column. 

If you don't have memory-cards, mM will create them for you under SAVEDATA subfolder in the game folder.

Use the following structure format:

/dev_hdd0/PS2ISO/Test Game (simple naming format - no cover download)

/dev_hdd0/PS2ISO/Test Game/ISO.BIN.ENC

/dev_hdd0/PS2ISO/Test Game/COVER.JPG (not mandatory, but if present will have higher priority than downloaded covers)

/dev_hdd0/PS2ISO/Test Game/SAVEDATA/SCEVMC0.VME (mM will create it if missing)

/dev_hdd0/PS2ISO/Test Game/SAVEDATA/SCEVMC1.VME (mM will create it if missing)

or even better, the recommended format:

/dev_hdd0/PS2ISO/[SCUS-97194] NFL GameDay 2003 (mM will use the gameID and will download the cover if available)

/dev_hdd0/PS2ISO/[SCUS-97194] NFL GameDay 2003/ISO.BIN.ENC

/dev_hdd0/PS2ISO/[SCUS-97194] NFL GameDay 2003/COVER.JPG (not mandatory, but if present will have higher priority than downloaded cover)

/dev_hdd0/PS2ISO/[SCUS-97194] NFL GameDay 2003/SAVEDATA/SCEVMC0.VME (mM will create it if missing)

/dev_hdd0/PS2ISO/[SCUS-97194] NFL GameDay 2003/SAVEDATA/SCEVMC1.VME (mM will create it if missing)

Basically you only need the ISO.BIN.ENC and nothing else:

/dev_hdd0/PS2ISO/MyPS2Classic/ISO.BIN.ENC

and mM will show "MyPS2Classic" disc icon in the RETRO column. If you name your folder with the game-id, mM will download the cover. If you put "COVER.JPG" next to the iso, mM will use it instead. That's it.