Usually, for a new agent installation you can just copy the directory of existing agent to a new place with the exception of its "temp", "work", "logs" and "system" directories. Then, modify
conf/buildAgent.properties with a new "name", "ownPort" , "workDir", and "tempDir" values. Please also clear (delete or remove value) for "authorizationToken" property and make sure "workDir" and "tempDir" are relative/do not clash with another agent.
If you want to install additional agents as services under Windows, do not opt for service installation during installer wizard or install manually (see also a feature request), then
<agent>\launcher\conf\wrapper.conf file so that
wrapper.ntservice.description properties have unique values within the computer. Then run
<agent>\bin\service.install.bat script under user with sufficient privileges to register the new agent service.
See above for the service start/stop instructions.