To take a screenshot on a Mac, you can use the built-in Screenshot app. This app allows you to capture the entire screen, a specific window, or a selected portion of the screen. Here is how to use the Screenshot app to take a screenshot on a Mac:

1. Open the Screenshot app by pressing the Command + Shift + 5 keys on your keyboard. This will open a control panel at the bottom of the screen that allows you to choose the type of screenshot you want to take.
2. To capture the entire screen, click the Capture Entire Screen button in the control panel. To capture a specific window, click the Capture Selected Window button, and then click on the window that you want to capture. To capture a selected portion of the screen, click the Capture Selected Portion button, and then click and drag your mouse to select the area that you want to capture.
3. Once you have selected the area that you want to capture, the screenshot will be taken automatically. The screenshot will be saved to your desktop by default, but you can also choose to save it to a different location or copy it to the clipboard.