Hi Swarna,

Software Counters are part of ServiceNow's legacy SAM product offered with ITSM to customers before the Jakarta release.  If you are utilizing SW Counters then you are using a product that is still supported for customers who purchased ITSM prior to the Jakarta release.  Current offerings are SAM Foundations, a basic SAM Solution offered to ITSM customers starting with London and beyond as well as SAM Pro, a robust subscription based product initially available in the Jakarta release.

To answer your question, once any of the three SAM Products mentioned above are installed, software installation data imported by either ServiceNow Discovery or through the Microsoft SCCM plugin, is written to the cmdb_sam_sw_install table.  When you click the "Count Licenses" button type UI action on the Software Counter form, a computation of available licenses subtracting software installations is completed.  Rights Used will then be populated with the number of rights consumed by software instllations.  If this is not happening in your instance, then you likely do not have Software Installation records or you've not configured the manual link between the Discovery Model and the Software Model table.  

The data structure required to return a license position in a counter record is as follows.

SW Installations are linked to Discovery Models (automated step).  Discovery Models are linked to SW Models (manual step).  SW Models are linked to SW Counters (manual step).