Value is the discount amount — a dollar figure for the fixed types, or a percentage for the percentage types.

Minimum Cart Value Required ($) is the smallest order subtotal on which the coupon works. If the customer's subtotal is below it, the coupon is refused with the message "This coupon is only valid for checkouts min. $X". Leave it at 0 for no minimum.

These two fields form the coupon's base rule; any Dynamic Custom Rates you add sit on top of it (a tier whose minimum is lower than this base minimum is ignored).