Currently, the menu supports mempak saves as an image of the entire mempak, not individual saves. It can list the individual saves, but not read/write them (yet). The save manager is entered by going to the SD browser (you probably start there) and pressing the Left Shoulder button. You then use the left/right shoulder buttons to change which controller pak is currently shown, and select "Raw MemPak" to save/restore the entire mempak to/from the SD card. Make note of the help info at the bottom of the screen showing what buttons do what.
As to cheats... I don't remember offhand. Let me look that over and get back to you.
EDIT: The current menu doesn't have cheat handling... I think we put it off until some other things were done because you could pre-patch roms with something like ucon64, saving them to the SD card. I'll work on a GameShark code handler this week.
EDIT 2: Now I remember... the GameShark codes are mostly on ram. To support this, we'd have to copy code "somewhere safe" and patch the loaded rom so that certain exceptions went first to this code before going to the game. That would allow us to use exceptions to patch ram locations. We never got around to working on that.