Thumbnails are very useful, but they take a little bit of time to make. All you need is a graphics editing program that has functions to resize an image (sometimes it's under a function called image attributes). Be advised--when you have made a thumbnail, you will need to save it as something different than the original. Also, you will generally want to link to the larger graphic when you are done.
Here are the steps:
1. Load a copy of the image into your graphics editing program.
2. Determine the ratio the thumbnail to be. (Do you want it to be half the size? One third of the size? One quarter of the size? One tenth of the size?)
3. Find the resize (or change attributes) function of your program. Most programs will recogize a percentage, for example you can type in 25% for height and width if you want the thumbnail to be a quarter of the size. (It it doesn't do percentages, you can calculate it by multiplying the pixels by the percentage. If you have a graphic that is 400 by 100, and you want it 25% of the size, multiple each measurement by .25. In this case, you'll get 100 and 25.)
4. Once you are satisfied with the thumbnail, think of a name for the image. Choose Save As and enter that name. (Tip: I like to just add t after the image name. For taco.jpg I'd use tacot.jpg)
5. Upload the image to your site, and edit your HTML to load the new image name with the new, smaller size. If you wish, you can link to the larger image around the image.
Example: You have taco.jpg which is 400 pixels wide and 100 pixels high. You made a thumbnail of it called tacot.jpg, which is now 100 pixels wide and 25 pixels high. After you have both images uploaded, here's the code:
<a href="taco.jpg"><img src="tacot.jpg" width=100 height=25 border=0 alt="click for larger taco"></a>
You'll find border=0 to be helpful in eliminating a link-colored box around your thumbnail.