getElementByName(elementName); // reads the form input elements that have a specific name reference. This returns an array of elements
getElementsByTagName(theTageName); // reads a set of tags, example input, div, p, and so on
getElementByClassName(cssClassRef); // reads any tag that has the matching class tag attribute set, not yet 100% compatible in some older browsers
getElementById(idTagName); // reads a specific element by its unique ID tag name.
if you google them, you will find how to use them effectively, note that the getElementsByClassName will require your code to have a workaround method in case it does not exist on the clients machine.