Settlements include all of your orders, but not any refunds. Funds will "settle" into your account after the settlement period. We group orders with the same settlement date together, and the dates are determined by business days. For example, all of your orders placed on a Saturday and Sunday would have the same settlement date.
The settlement step is essential, as some merchants use the interest-bearing account instead of the automatic deposit plan. So the "Settlements" tab will show the dates all funds are available, and it will say whether or not they go into the automatic plan or the interest plan. On that tab, the settlement date is on the left. You can see the ones that are upcoming (Pending) and the ones that have been completed (Processed) by selecting the appropriate tab. You can then click on each settlement to see the details of the orders that were included in the settlement. The ones that are on the Processed tab and are not for the interest account will then show up on the Withdrawal Account page.
However, the "Withdrawal Account" tab provides more in-depth information - it shows refunds, among other changes. We deduct refunds from the next upcoming deposit, rather than pulling them out of your bank account. The "Overview" tab on that page will show you the exact breakdown of the funds sent to your account, including things like referral bonuses and refunds.
Your Withdrawal Account can be negative if you've issued refunds and have not since had enough orders to make up for those refunds. Funds will not be transferred to your bank account until that Withdrawal Account balance is positive again.