I just went through installing an additional polling engine, and was also confused by the instructions. Here are my notes:
1. Extract the zip on your remote server.
2. Run the Solarwinds-Orion-AdditionalPoller executable on your remote server.
3. The first part of the install process asks for the address of your main server, and a user to log into your main server with.
4. The installer then checks all the requirements are met from the main server and installs the appropriate components.
5. The license dialogue appears after installation.
6. Either license, or use the 30 day eval, but don't think you are done at this point. Wait patiently for the Configuration Wizard to appear. Don't let the server restart for patches, like I did the first time.
7. Configuration Wizard will start, and configure the necessary components, provided your remote server has access to your Database.
Once installed, the additional poller should appear in the Web GUI from your main server. After I had the additional poller installed I ran into a couple of other issues. The poller appeared on the main server, but the main server could not access the Orion license information on the additional poller, and NCM couldn't access the additional poller either. I had to add a host entry on the main server to point to the IP/FQDN/Name of the additional polling server, and I also had to open port 17777 on a firewall between the main server and the additional poller. If things don't seem to be working correctly, try using telnet from your main server to connect to port 17777 on the additional polling server.