This document describes in detail the Steps for Installing Oracle Management Agent (Management Agent) 12c using a response file. You can also refer to Enterprise Manager Advanced Installation Guides on OTN from the following links (these are authoritative sources in the case of a discrepancy):
Installing a Management Agent in silent mode is only an alternative to installing it using the Add Host Target Wizard. The silent mode requires you to use a response file for providing the installation details and a deployment script (agentDeploy.sh) for silently installing the Management Agent using the information supplied in the response file.
Installing in silent mode is best suited when you want to install an additional Management Agent on a destination host, from the destination host itself, and without using the Add Host Target Wizard in the Enterprise Manager Cloud Control.
See the following Oracle Webcast for a demonstration of Silent EM Agent deployment using the agentDeploy.sh method, as well as other silent methods: