If the Philae lander (named after Philae Island in the Nile where an obelisk was found and used, along with the Rosetta Stone, to decipher Egyptian hieroglyphics) lands successfully, the British-built Ptolemy will measure stable isotope ratios of key volatiles on the comet's nucleus (whatever that means).
The comet has very little gravity, so the Philae lander may just bounce off the comet. But if it does land sucessfully then little drills will emerge from Philae's legs and drill into the comet to anchor Philae in place. It will also use harpoons to anchor itself.
Ptolemy
Philae lander
Any second now.....
This picture from Rosetta's Osiris instrument shows the Philae lander on its way to the comet