Go to the Desktop

The Desktop contains icons which take you to the main applications on your PC.
Press Windows key + D to go straight to the Desktop.
It will not close the applications, it will just minimise them to the Taskbar.
If you press Windows key + D again, it will bring focus back to the application you were working on.
Once on the Desktop, you can Arrow to the application you want or press the first letter, then press Enter to open.
Some people also use Windows key + M to minimise all applications. But this does not have the same functionality. If you press it again, it will not switch back to the applications that you working on.