To cycle (switch) through open programmes (applications) in Mac OS, press Command and hit the Tab key.
You will see the large icons of all the open programmes in the middle of the screen. One hit on the Tab key will move you from the programme you are in to the one you’ve been using before that.
Continue pressing the Tab and you will ‘cycle’ through the programmes. Cycling goes to the right.
But if the programme you want to switch to is on the left, press Command and Tab and hit the left arrow on the extended keyboard. If your keyboard doesn’t have arrows or if you simply don’t like arrows, Press Command and Shift and then hit Tab. Switching will go to the left.
Cult of Mac site suggests doing left-cycling by pressing Command and Tab and then typing tilde (~), which on some keyboard sits in the top row to the left of figure 1. I don’t have it on any of my keyboards, so cannot verify it.