how to use MMC card
hmmm... i think there are some sites out there that teaches you how. basically you first need to get comfortable with SPI. are you planning to use a file system to store data on the mmc (i.e. you want your data to be readable in Microsoft Windows)? if yes, then you will also need to understand the FAT32 file system. but i guess you just want to be able to write some few bytes on the MMC first. if you are using PIC MCU, the mikroBasic compiler from mikroelectronika.com has built-in functions.