1. is a Community Builder (CB) plugin. As I understand it, when data is entered in CB profile (name, email, avatar, etc), it triggers the plugin, which then transfer the data (synchronises) to the corresponding Moodle profile.
2. is a Joomla plugin that allows Joomdle to use CB profile's data. In Joomdle's Configuration page, under the "User profiles" tab, you can set additional data source for Joomdle to get data from. For example, this allows mapping of custom fields in CB to fields in Moodle profile (Joomdle > Mappings).
They are both strictly not required for Joomdle to function, but are additional features and better integration when you use CB as well. Eg, when you disable 1., the CB profile and Moodle profile won't be synchronised, but you can still use Joomla/Moodle because the data (mostly) does not affect its functions.
