manage_agents is available in two versions:
The purpose of manage_agents is to provide an easy-to-use interface to handle authentication keys for OSSEC agents. These authentication keys are required for secure (encrypted and authenticated) communication between the OSSEC server and its affiliated agent instances.
Display the help message.
Display OSSEC Version.
List available agents.
Extracts key for an agent (Manager only).
Import authentication key (Agent only).
The OSSEC manual goes into details on usage of this command at Working with Agents