Q:

CSS attribute and tag attribute

I am studying now HTML and CSS. I have this code in CSS:
h2 {
    background: url(../_images/open.png) no-repeat 0 11px;
    padding: 10px 0 0 25px;
    cursor: pointer;
}

This code changes some attribute values of all h2 tags. 
My question is:
How do I know what attributes a tag has, so I can make use of them?
For example, if I use all h3 tags for example, where (on the Internet) do I find what attributes the tag h3 has, so I can change them? I may want to change the cursor, but how do I know an h3 tag even has a cursor attribute?
Something like when using a Button from WindowsForms, I go on MSDN and find all the properties that a Button has and I set them as I want.
I
 checked on w3schools, but could not find anything like that.

A:

This code changes some attribute values of all h2 tags.

You appear to be confusing CSS properties with HTML attributes. There is some cross-over between the two, but they should be considered separate things.

How do I know what attributes properties a tag has, so I can make use of them?

You can set any CSS property for any element. Some will always apply. Some will apply depending on what other CSS properties are set. 
For instance, left only applies to elements that are positioned (which is defined as Having a position property value other than static).
The element type doesn't matter (beyond the values for properties that are assigned to it from the browser's default stylesheet, and usually the only one that matters there is display).
The CSS 2.1 specification a a list of all the properties  you can use. CSS Level 3 adds more properties, but they are scattered throughout various specifications. The W3C has a wiki, but I can't speak for its completeness. 

