Screenshots in macOS Mojave deliver new on-screen controls for easy access to every screenshot option and new video recording capabilities.
Press Command + Shift + 5 on your keyboard to bring up the screenshot toolbar, then choose either Record Entire Screen or Record Selected Portion. Your recording will begin immediately if you select Record Entire Screen.
If you're only recording part of a screen, use the mouse crosshairs to select the portion you wish to record. Your recording will begin immediately after make your selection.
Press the Stop button in the Menu bar to stop the recording.
Control-click, right-click, or two-finger-click on the recording that appears in the bottom-right corner of your screen.
Use the contextual menu to choose where to save the screenshot (Desktop, Documents, Clipboard, Mail, Messages, Preview, etc., send it, show it in the Finder, delete it, or mark it up.