Weird Sap-Like Creatures on Naval Orange Plant?

Wow, those are freaky looking! We don't have anything like that here in Minnesota, but if it is a scale, they can be hard to get rid of. If your plant isn't too large, I would start by hand picking/squishing them. If that isn't possible you need to find an insecticide that will kill them. It will probably take multiple applications until you get them under control. Most adult scales have just what their name implies, a hard shell like covering that protects them.