Go to the Settings tab and find the "Eye-Fi Cards" section. Tap the "Add" button and a new window will appear:

Give the card a name - anything will do - and then enter the ten-letter Activation Code that is on the EyeFi Mobi card case. Tap "Add", and you will be asked to install a network profile. This is needed to let the iPad connect to the EyeFi Mobi card. There will be several warnings saying that the profile is not signed, which you will need to accept.

Finally, in the EyeFi Setup section of the Settings tab, make sure that the "Enable Eye-Fi Server" setting is on.