The Ctrl-Alt-Delete keys have several functions. Which one do you need to perform on Mac?
If you want to close an unresponsive app, press the Command-Option-Esc keys, and the list of running apps will be displayed. You can choose the one that's not responding and click "Force Quit" to kill the application.
If you wish to open an equivalent app to Windows's Task Manager, which shows you how much CPU or memory an application consumes, you need to open Activity Monitor. There's no shortcut to launch it. To open Activity Monitor, you need to access the Applications > Utilities folder.