How can you add images into a css class and display it using span tag?

You would give the CSS class a background of that image, then assign it using a class attribute in your span tag. For example, your class's name will be class1, and your image will be named 'myimage.jpg'.
CSS:
.class1{
background-image:url('myimage.jpg');
}

Then, for your HTML span tag:
<span class="class1">
Add a lot of '&nbsp;' here until you can see your image.
</span>