Every proxy entry is written as an IP address paired with a port number, and the port matters just as much as the address for actually connecting.
What a port does here
A single server can run multiple services on different ports, so the port number tells your device exactly which service on that server to talk to — in this case, the proxy service specifically, not whatever else might be running on that machine.
Common proxy ports
8080 and 3128 are the most common defaults for HTTP proxies, while 1080 is the traditional default for SOCKS proxies. These aren't strict rules — a proxy can technically run on any port — but seeing one of these numbers is a reasonable hint at what type of proxy you're looking at.
Why it matters when configuring
Entering the right IP with the wrong port simply won't connect. If a proxy fails immediately rather than timing out, double-check the port matches exactly what the list specified.