Choose the system that you are using:
Android
To take a screenshot on an Android device, such as a Samsung phone/tablet or other non-Apple devices is pretty simple as long you follow the below steps:
Press the Power button and the Volume Down button at the same time, your screen will go white for a brief moment and the screenshot will be saved to your device's galler.
Should that not work try pressing the Power button and the Volume Up.
iOS (iPhone/iPad)
When taking a screenshot on an iOS device be sure to follow the below steps:
Press the Power button and the Volume Up button at the same time, your screen will flash white for a brief moment and the screenshot will be saved to your photos, this can be accessed from your "Photos" App.
If you are on an older device which has a home button on the bottom of your phone you will need to press the Home button and the Power button at the same time.
Windows
To take a screenshot on a Windows PC there are a couple of different ways in which you can do this.
One way of doing this is by holding down the Windows Key 
SHIFT and S at the same time, your screen will darken slightly and you can select an area that you wish to screenshot by holding down the left mouse button and dragging your cursor.
Once you let go of your left mouse button the screenshot will be saved onto your clipboard and you can paste this onto a chat or email by right clicking your mouse and clicking "Paste", alternatively you can also do this by clicking the CTRL button and V.
Windows has a built in program for this, if you go to your Windows Search and search for the "Snipping Tool", then click "New" you'll be able to select the area you want to screenshot just like the previous method.
After you have selected the Area you can either click the "Save" button 
to save the file on your computer to upload it, the image will also be automatically copied to your clipboard if you want to upload it by pasting the image instead, this can be done the same way that was mentioned earlier.
Mac
How do I take a screenshot?
Hold down the Command Key and Shift Key and press "# 3 Key". Your Mac captures the entire screen and saves it as a file on the desktop. The file name will look like “Screen shot 2024-08-06 at 08.45.00 AM.png”.
How do I take a partial screenshot?
Hold down the Command Key and Shift Key and press "$ 4 Key". Use your mouse to draw a rectangle in order to specify what to capture – or press the spacebar and then click on something (e.g. a window) to capture it. Your Mac then saves it as a file on the desktop. The file name will look like “Screen shot 2024-08-06 at 08.45.00 AM.png”.
Where is my Screenshot?
You will find the file on the desktop. Also the Finder might be helpful.
Can you show me in a video?
ChromeOS
How do I take a screenshot on my Chrome OS device (e.g. Chromebook or Chromebox)?
Hold down CTRL Key then immediately press and release F5 or the Switch Windows Key = Your Chrome OS device captures the entire screen and saves it as a file into your Downloads folder.
How do I take a partial screenshot?
Hold down CTRL Key then immediately press and release F5 or the Switch Windows Key = Your Chrome OS device captures the entire screen and saves it as a file into your Downloads folder.
If it works, what does it look like?
Can you show me in a video?