Knowing how to capture all or part of the view of the computer screen and save as an image file is a trick that everyone needsd to know. I frequently capture pictures and diagrams from PDF files (think past Regents exams) that are part of the public domain but not so easy to edit unless you take a screenshot. I also ask my students to use screenshots when they are completing work online and the end result doesn't produce a usable file (results from PhET interactives, certificates from simulations like Virtual Earthquake, etc.). The problem becomes when you work with multiple types of devices and operating systems... there's a way to take a screenshot on everything but the technique is just a little different.
Chromebooks:
Newer Chromebooks have function buttons across the top row of the keyboard much like other laptops, but they might look a bit different than what you're used to. Older keyboards have the traditional function buttons (F1, F2, etc.) which may or may not have the picture icons. The window button (or F5) is the one you'll need to take a screenshot. (Note: without the Ctrl key, this button advances you to the next window you were viewing.)
These screenshots get saved to the Downloads folder as images, or you can click on the "Copy to Clipboard" link that pops up right after the screen capture.
Click here for a full tutorial on using the screenshot function on Chromebooks.
Windows OS:
Lots of people know about the print screen button on Windows keyboards, but for some reason not many people know about the Snipping tool. To access it, use the search box and type "Snipping Tool" - you can always pin it to the taskbar if it's something you'll use frequently. The neat thing about this tool is that you can capture the entire screen, a rectangular portion, or something totally free-form. You can add text and drawings to annotate the screen capture as well, and it prompts you to name the file and choose the save path (which makes it more likely that you'll remember where it goes). You can also share (by email, etc.) directly from the Snipping Tool.
Click here for a full tutorial on using the Snipping Tool in Windows.
Mac OS X:
Like Chromebooks, Macs utilize a series of keyboard commands to take a screenshot. The command button
Command + Shift + 3 ... takes a screenshot of the whole screen
Command + Shift + 4 ... lets you drag a box around the area you wish to screenshot
Command + Shift + 4 + Spacebar ... brings up a camera icon that lets you choose a specific window you want for the screenshot
Screenshots are saved to the desktop as .png files, which makes it particularly useful for dragging and dropping the files somewhere (like into a document or into Google Classroom to turn it in).
Click here for a full tutorial on how to take a screenshot on a Mac.
iPad or iPhone:
It's pretty easy to get a screenshot on an Apple device; simply hold the Home button and the Power button at the same time, and the device takes photo that automatically gets saved to the Camera Roll.
From there, it's accessible as a photo to upload (either from the Photos app as an upload option, or by accessing the Camera Roll through whatever app you are using - the Google Classroom app and Google Drive app both will allow you to access your photos).