Ubuntu - write instructions to add multiple IPs to 1 Server / network interface

I'm looking for someone to explain exactly how I can add multiple IPs to one server. The server is an instance on EC2. I have linked 2 Elastic IPs to the Ubuntu server. The first IP is working, however the second IP times out. After doing some searching I'm getting mixed results. Apparently I need to add an eth1 to my second IPs private IP address. That's where I get lost. You will be my go-to tech guy if you do this well.. Shouldn't take longer than an hour.