What's the Difference Between Memberships, Clubs, Packages, and Signups?

Memberships:
These are your actual club members. In this section you can see who belongs to your different clubs, you can dive into each member, cancel their club, put their club on hold, adjust shipping, billing, payment info, etc. 

Packages:
These are your monthly/quarterly/annual shipments. Here you can set up shipping dates, user-choice parameters, default bottles, etc for your monthly club package. You can also process your club packages in here. 

Clubs:
These are the clubs that members sign up to on your front end site. IE - red club, white club, 12 month club, etc.

Signups:
These are your site visitors who have started but not completed a club signup. These signups are similar to abandoned carts - you can email them to try and figure out why they never finished signing up.