When I switched school districts, I moved from having to use Microsoft to Google. This meant that all my PowerPoints needed to be reworked for use in Google Slides. It is actually very easy to move a presentation from PowerPoint to Slides and it takes just a minute.
First, open your Google Drive. Near the top left of your Drive, click the New button.
You will get a dropdown menu when you click New. Select File Upload from the dropdown.
Select the PowerPoint file you want to open in Google Slides. (You can follow these same steps for other document types as well.)
Once you open the PowerPoint file, you will see a small box pop up in the bottom left of your Google Drive that will let you know when the file upload is complete.
Once the upload is complete, click on the file. You may see the message below as Google opens the file in Slides.
Then, your PowerPoint will open in Google Slides and you are ready to go!
You will want to check each slide to make sure no formatting errors occurred. Sometimes font sizes or types can come out slightly different when you upload the PowerPoint into Slides.