Screen capturing tools allow you take a quick picture of what you are looking at on your computer. It's a fast, easy way to save images that you may want to use later for a multimodal composition. Just be careful to be sure that the images you are using aren't violating someone's copyright. There are many ways to find copyright free and creative commons images that won't get you in trouble. The Finding and Using Images and Video tab in this guide can point you to some resources for this.
Windows comes with a program called the Snipping Tool. You can use it to capture anything that you can see on your desktop. It's a good idea to lock it onto your program bar so you can get to it easily. Here is a short guide to finding and using it.
Mac users can press COMMAND+SHIFT+3 simultaneously to save an image of the entire screen to the Desktop. They can also use an application called Grab (for OSX operating systems) that has some more options.
Screencastify allows you to capture video of your Chrome browser window. It is a Chrome extension that you can download for free. You can also grab audio and, if you have a webcam, you can include video of yourself talking while you explore the Websites.
