You have 9 riders per team. The cyclist who has the number ending in 1 is the team leader - Nibali is 51, Wiggins is 101 etc etc
The other 8 work for the team leader as the tour starts, or for the sprinter if the team is unlikely to challenge for General Classification. Froome is the number 2 at the moment and so his job is to protect Wiggins in yellow. If Froome had not been held up in a crash in the first week that cost him 90 seconds, and had been a bit closer to Wiggins in the time trial it might have been every man for himself as they would be very close, but the important part was for them both to take those last few seconds out of Nibali and kill the thing stone dead. They will get a stage win tomorrow.
Domestiques are the "other riders" of a team. They collect water bottles for the leaders, and set the pace up the mountains like pacemakers in a 1500 metres. Ritchie Porte, Edvald Boason Hagen, and Mike Rodgers are the Sky domestiques in the mountains.