You can create sections in Web Application, in Administration – Document Management – Records Classification Scheme(fig. 1).
Fig. 1. Add Section button
After you click on this button, a dialog box opens, where you have to enter the section name. If you need a prefix to be added to the document registration number, specify it in the Index field (fig. 2). This prefix will be displayed only an index is not specified in the category settings or the {$ParentIndex} variable is selected in the Number Template field.