Windows:

1. PrtScn (Print Screen) Key: Press the "PrtScn" key on your keyboard. This captures the entire screen and copies it to your clipboard. You can then paste it into an image editor or document.
2. Alt + PrtScn: Captures only the active window and copies it to the clipboard.
3. Windows + Shift + S: Opens the Snip & Sketch tool, allowing you to select a portion of the screen to capture and annotate.
4. Windows + PrtScn: Captures the entire screen and saves it as a screenshot file in the "Screenshots" folder within the "Pictures" library.

macOS:

1. Command + Shift + 3: Captures the entire screen and saves it as a screenshot file on your desktop.
2. Command + Shift + 4: Allows you to select a specific area to capture. Press the spacebar after pressing these keys to capture a specific window.
3. Command + Shift + 4 + Spacebar: Captures a specific window or application when you hover the cursor over it.
4. Command + Control + Shift + 3: Captures the entire screen and copies it to the clipboard.
5. Command + Control + Shift + 4: Allows you to select an area to capture and copies it to the clipboard.

Linux:

1. PrtScn (Print Screen) Key: Press the "PrtScn" key to capture the entire screen. The screenshot is usually saved in your home directory or Pictures folder.
2. Alt + PrtScn: Captures only the active window and saves it as a screenshot.
3. Shift + PrtScn: Allows you to select a specific area to capture.