In a moderated list, a human goes through the messages before they are posted to the mailing list. This may be as simple as just keeping the junk out of the list or as complex as editing the messages for content and organizing them into an indexed format. Messages sent to moderated lists can be delayed while waiting on the moderator. Messages sent to an unmoderated list are not filtered in any way. Unmoderated lists are more common, since they are easier to set up and don't require a human's valuable time.
Mailing lists can be in the digest or non-digest format.
The instructions that will be sent to you will show you how to set the format. They frequently have a table of contents and sometimes even page numbering. Generally, digest format is much more convenient, since some mailing lists generate hundreds of messages per day. With the non-digest format, every message that goes to the list goes right to your mailbox. This can be very inconvenient, since each message must be read and deleted individually.