Once you have created your coupon, if it has not been applied to the Total, you can apply it to specific levels. Click on the row of the coupon, then check the applicable boxes to apply it to all or just specific levels.
A coupon can be attached to multiple levels and multiple coupons can be attached to the same level. Coupons only apply to ticket levels and not fees or add-ons. Only one coupon can be used per transactions.