You can insert an Image into your document from the Insert drop-down menu. It will allow you to browse and choose from pictures already on your computer, or you can insert a picture from the web by inserting the URL.
You can manage the size of the image, its alignment, and text-wrapping by clicking on "More image options" right below the Browse window.
You can also find images on the web to help illustrate a word in your text. You'll find this feature under the Tools drop-down menu. First, highlight the word you would like to find an image for, then, choose Tools and "Search the web for word."
Before you insert an image from the web, be sure you have permission to use the image. Please check the Fair Use Guidelines for Multimedia. Now days, many images are shared under a Creative Commons license. You'll notice that these images are "labeled for reuse." I found them by choosing "Advanced Image Search" from the right of the "Search Images" button. I then choose "labeled for reuse" in the "Usage Rights" drop-sown menu.
Google also offers a number of other options in Image Search. Find these under the "Show Options" drop-down menu on the left hand side of the image results page.
Look for images by size, type, or predominant color.