I guess you already have observed that an account belongs to a group (type). A group (type) belongs to a class.
Depending on how your country wants to present the balance sheets and profit and loss statements, you can build these rules with help of groups (types) and classes.
When a balance sheet is printed it is sorted on 1. class, 2. group(type) and last the account itself.
As you see the accounts are not necessarily printed out in account number order.
First the Title for the first Class is printed, Then the Title for the first Group is printed. Then the accounts within this group are printed. When a new group is coming, the totals within the old group group is printed before the title of the next group is printed.
The same thing happens when a new class is coming. The total for the old class is printed and the title of the new class is printed and so on.
By arranging the groups you can present your balance sheets and PL statements your own way.
By also using sub-groups (a group belonging to another group) you can create even more sophisticated aggregators. But this is more acvanced.
This sticky topic explains how you make a rearrangement of new groups and classes, should you need more space between the group/class id's.
/Joe