html is the page description language used on the world wide web -- that is, what most web pages are written in. If you view the "source" code of a web page, html is what you see. (in IE, go to "source" in the View menu.)
Basically, html tells the browser how to display the content of the web page, using "tags" (markers inside angle brackets) like
to center text or objects. There's a lot to it (as you might guess from looking at the source code for a typical web page).
Java is a programming language which is commonly used on web servers (the computers where web pages are stored and transmitted to your machine) to run interactive web sites. (Other languages used for such things include Perl (cgi), PHP, ASP...) Java differs from the others by transmitting a copy of the program to your browser and running it there, while the others run the program on the server. These are used for things like processing user input from forms on the web page, accessing databases, and so on.
Any of these programming languages, when used on the web, sends your browser something in html format, with headers, tags, and so on, so your browser only has to interpret one form of data to display a web page.
JavaScript (which you may be thinking of) has almost nothing to do with Java. This is a scripting language which can be included in html files, which can run a number of relatively simple things, like highlighting buttons when you roll over them, or validating that the info you've entered into forms is complete, etc. If you look at the source for a web page, the tag
