You can change the background of your PowerPoint slides using the "Format Background" feature located in the "Design" tab.

You can improve your PowerPoint presentations by both improving your presentation skills and making better use of the program ...

Google Slides provides a good bang for your buck. It’s a good-enough presentation tool with an intuitive interface and unmatched collaborative features.

To manually crop a picture in Microsoft Word, Excel, or PowerPoint, select it, and in the Picture Format tab on the ribbon, click the top half of the split "Crop" button.