If you mean your own artwork, then you'd take a picture of it, upload it to your computer (make sure you know where you're saving it), then select Insert > Picture in Word, browse in the location where you saved the photo, click the picture, and insert. If you mean an image from the internet or something, you can just save it to your computer and basically follow the rest of the steps above.
Be careful: most Creative Commons images require attribution, meaning you need to give credit to the artist in order to use the image. Make sure you understand Creative Commons and other licenses 3 Popular Image Licenses You Need To Be Familiar With Before Using Someone's Photos 3 Popular Image Licenses You Need To Be Familiar With Before Using Someone's Photos Read More before using such images.
As an artist I resent some people's assumption that original art from my abilities and imagination, which I have sacrificed a lot to develop, should somehow default to public property. If we require artists to participate in a money economy their art belongs to them. Copying images and not following the copyright owners permissions to the letter is stealing, outright. And deep pockets like Disney has taught individuals that the hard way.
To download the clip art and animated GIFs on this site, just move your mouse over an image or animation and right-click. Then select "Save Picture As..." (or "Save Image As" if you're using a Mac). Feel free to open the pictures in your favorite graphics software, such as Photoshop, Fireworks, Gimp, etc... and edit if you wish. Keep in mind that linking to these images is not permitted.
This is TERRIBLE! Besides being able to edit vector images like Will mentioned (which is important for those of us who don't have graphic artists available to create custom images or the budget or time to buy that service ad hoc), you could also search for style "families" (different graphics that were all in the same style). There was a huge range of files and styles in the collection and it was much faster to find what you need than to do a Bing search. Plus, you knew that everything there was free and free to use, without having to worry about CC license issues.