The most basic method of image positioning starts with including the <img> code in the HTML text in define_main_page.php in the general area you want it to appear - top, middle, bottom. Don't hard-code "right" or "left" in the PHP file; give each piece of image code its own unique id.

Then edit your stylesheet to add (for example):
Code:
#homepage {
    float: right; /*this makes it move all the way to the right*/
    margin-right: 30px; /*this clears 30 pixels of space on the right of the image*/
    margin-bottom: 12px; /*this clears 12 pixels from the bottom of the image*/
    }

#homepage2 {
    position: relative; /*this makes it move relative to where it would normally sit*/
    top: 8px; /*this moves the image 8 pixels down from the top*/
    left: 13px; /*this moves the image 13 px away (to the right) from the original left edge*/
    }
There are many other things you can do. The best plan is for you to look at www.w3schools.com which has basic tutorials on HTML, CSS and PHP. Refer back to that when you want to know how to do a specific thing. It also has interactive examples where you can instantly see the effect of trying different versions of a command.