Powerpoint 

Powerpoint will try to be clever and use both your screens in a "Presenter" mode by default. When sharing screens during a lesson its far better to tell it to only use one screen, leaving the other free for teams or other programs

During a Presentation

Step 1 - Start your powerpoint presentation, often it ends up taking both screens as shown below!

Step 2 - To swap the presenter view click on Display Settings and then Swap Presenter View and Slide Show. Alternatively click on Duplicate Slide Show to show the presentation on both screens.

Step 3 - To disable the presenter view click on the more options icon, then Hide Presenter View

Step 4 - To re-enable click on more options and then Show Presenter View

To be a complete pro you can setup all these settings before you start your slideshow

Step 1 - Click on Slide Show and then Set Up Show

Step 2 - Under Multiple Monitors choose the slide show monitor and decide if you want to enable presenter view.  This is unique to each slide show and will be remembered when you next open that powerpoint file.