At this level you will probably be using graphics that you have found somewhere on the Internet. Many, many places have graphics that can be used freely. First you need to copy it and save it in your directory. To do that, go to a page that has a picture that you would like to copy. You can save the image with the same name, or you can re-name it.
Graphic files have names with the extensions .gif or .jpg .
Once you place the picture in your directory you can make a link to it, or you can just have the image appear in your HTML page. Here is an example of an image I might put at the top of my home page. There are many ways to align the image in relation to the text. You can also draw borders around it. These are things you may want to do as you become more comfortable with HTML, and with a good HTML reference book in front of you.