Command tab will show icons for open apps. Hold the command key down, tap the tab key and then keep tapping it to get to the app you want to switch to and then release the command key.
Another option is Mission Control: See open windows and spaces in Mission Control on Mac - Apple Support
You can add Mission Control to the Dock at the bottom of the screen and then click it to activate it. Open a Finder window, click the Finder "Go" menu and then click Applications on that menu. That will open the Applications folder and you can drag Mission Control from there to the Dock. Other methods of opening Mission Control are described in the above support article.
Another option is the Dock. It can be set to show an indicator for open applications. See: Use the Dock on Mac - Apple Support