Why can't I and how can I read files on my Macbook?

Install the program on your computer, otherwise you’ll have to export them at school. Not experience but just common sense,

Check here to see if you have compatible software on your macbook.

You could also try talking to the IT people at your school. When I was in school, I had to have special programs on my MacBook in order to use the school’s online system because it was initially designed only for IBM compatible computers. If you talk to the IT people at your school, they may be able to look at your MacBook and get it all set up for you to use.

You should be able to view the Powerpoint files without installing any software by selecting them in Finder and pressing the spacebar to open Quick View. From there you can view all the slides but not edit them.

Another free option is to use Google Docs to upload, edit, view, and download Word and Powerpoint documents. Otherwise you will need to use Pages and Keynote from Apple or Microsoft Word and Powerpoint for Mac. As @Seaofclouds said, the school’s IT department should be able to set up your Macbook and possibly give you an educational discount if you choose the paid software.