f1

The dock at the bottom of your screen lists a bunch of applications that you have selected to display there. There are a lot more. You can see which apps are open by looking at the dock as well. Open ones have a glowing blue little mark underneath.
You can click on any of these apps and they will open, or if they are already opened, you will be switched to that app. Another way to switch apps is to use the Command + tab keys. Press the Command key, the on on the left of the spacebar, and hold it why you click on the tab. You can continue to click the tab key, while holding down the command key to move through all the open apps. stop and let go of the command key to select the one you want.
You can also scroll through the apps after clicking on the command + tab. Keep holding down the command key but don't click the tab button again. But this time, click the arrow keys. left arrow goes left, right arrow goes right.
Easy Peasy.