A dedicated IP is an IP address for a server that is reserved for only one server and isn't shared with others.
What this means is that you can use the default Minecraft port of 25565, which is optional to enter to join a server.
So you only have to enter in the IP without the trailing :port number.
If you have a URL redirect, it also means you won't have to append the port after the URL to join your server. This allows your server to appear more professional and is easier to memorize and join.