What is the difference between the Class attribute and the ID attribute in HTML and CSS?

An ID is used to define the style properties of a specific thing whereas a class is used to define something you may use multiple times. For instance, if you are going to make a loginbox you will use an id because you will only have one identical loginbox on the page whereas if you wanted every quote to be given the same style you would use a class, this would mean all elements with class=quote (after you define it in the CSS) would always style quotes to your needs. In short, you could use either as they have pretty much the same outcome, but organised CSS is good CSS so you are better off using classes and ID's as i have defined them above.