Not sure at what stage you are at...
you need to;
1 ) get the game files
2 ) copy the game files to the SD card (plug SD into the PC/connect with a cable and set to mass storage)
3 ) copy the scummvm.apk to the sd card
4 ) install a file explorer on your phone (from market place) - I use ES File Explorer
5 ) on phone: settings -> applications -> tick 'unknown sources'
6 ) browse using file explorer on phone to the scummvm.apk and install it
7 ) start scummvm when installed
8 ) add the file path to the game files you installed.
9 ) select game and hit start!
Is that a simple enough overview? - if you're stick at a particular part let us know and I'm sure someone will help
I was going from memory so some bits may not be 100% accurate.