Management licenses are sized based on the number of gateways that are managed. An CPSG-NGSM10 can manage up to 10 security gateways, for instance.
If you are using Endpoint features like SandBlast Agent, Full Disk Encryption, Endpoint Compliance, and Remote Access, the license also gives you the ability to manage those features for a certain number of endpoints. In the case of a CPSG-NGSM10, you can manage up to 1,000 computers.
In both cases, you must also have licenses for the relevant managed devices (gateways and/or endpoints). If you're not using the Endpoint features, you can ignore the number of Endpoints as it is not relevant in that case.