If you are coming from Windows or another desktop environment, you are likely familiar with alt-tab menus. To use it, hold down alt and press tab multiple times to toggle through a list of all open applications. Letting go of alt, pressing enter or click on an entry will switch to the application. You can also press tab just a single time and proceed to type in the application name. There is also a more visual version available. It can be accessed using Super+^ (the caret key) or by right clicking on the status bar in the top right.