The only numerical codes with any meaning are the activity event codes and object type codes. These codes are all documented here: Analytics Data Model
All other id's are just system generated surrogate keys and have no meaning - they are used for table join purposes. E.g., month_id is the key of the record in jivedw_month representing that month period and is used to join the the corresponding month_id column in the aggregate table. The attributes in jivedw_month can be used to select those time periods.