In handwritten accounts, Posting is the process of taking the entries written in, for example, the Cash Book, and transcribing them into each of the relevant accounts.
In the handwritten process it is possible to overlook an item. In this system you can have a similar situation if you have deleted an account name which has items already accumulated in it.
This window will give a list in Journal Entry format of all unposted items.
If you look at the two left hand columns of the display, you will find the account numbers under which each item is accumulated.
You will find in many cases that only one column is displaying a number for an item.
That means that only one of the two account numbers associated with every item has not been posted.
Every number that appears in the two left hand columns is a number that does not appear in your Account Names List.
Your first course of action should be to check whether you have deleted any account names incorrectly. If so, re-insert them in your Account Names List and then click 
Refresh Display button.
You can also use the push-button functions to correct individual items.
You may find when looking at this display that you see an item with arrows in the CR A/C column which point to the DR A/C column.
In this case you have specified both the "Comes from" - credit - and the "Goes to" - debit - accounts for this item as the same account. You will have to change one of these references.
NB. If you are working at the Professional level, the cause of your accounts being out of balance may be because you have deleted a VAT account containing automatically calculated VAT items.