The differences are pretty simple:
FortiCare: This is for the support of the FortiGate. You will get access to the firmware images for upgrades, online ticket creation and phone support.
FortiGuard: This is the collective name for the security subscription services of the FortiGate (Antivirus, AntiSpam, WebFiltering, Application Control, IPS).
When you get a bundle you get the FortiCare + FortiGuard (ie: you get the support, plus the security subscriptions).
Now not everyone wants/needs to get all the subscriptions. For this they have a few different bundle options available for all the bigger models (100D and up):
NGFW: Includes the IPS and Application control subscriptions
ATP: Includes Webfiltering and AntiVirus
NGFW + ATP: Includes IPS, Application Control, Webfiltering and AntiVirus
UTM: Includes IPS, Application Control, Webfiltering, AntiVirus *AND* AntiSpam
All the above bundles comes with FortiCare (ie: support).
Hope that helps!