HTML is used primarily for internet use. This is the base of almost any website because of it's versatility.
All of the Cs are used for pretty much any application. I'm not very familiar with C, but I'm pretty sure it's the most complicated to learn because of how much you can do with it. However, this is just based on what I've heard.
Java is probably the widest used code because of flexibility. Java can not only be used in succession with HTML but is also (as far as I'm aware) universal, so every OS can run it. Usually, it is used for interactivity on websites along with flash, which is very similar.
This is my knowledge of these languages, and learning them is all based on what you want to do. If you want to design web pages, HTML is very important and needs to be understood, because it is the basic language of any website.
This is just a very broad description of each, and I am not very fluent in C or even JAVA.
If I have made any mistakes in my descriptions, I'm sure an expert will correct me
Hope it helped a little