If you have existing presentations that you created in another program, you can import and convert them to Slides to collaborate with your team.
Go to Drive.
Click New > File Upload and choose a presentation from your computer. Supported files include .ppt (if newer than Microsoft® Office® 95), .pps, and .pptx.
Right-click the file you want to convert.
Select Open with and choose Google Slides.
Converting a presentation from another program creates a copy of your original file in Slides format. You can then edit it in your browser like any other Slides presentation.
Have a PowerPoint presentation?
If you've already stored Microsoft PowerPoint® presentations in Drive, you can also update them without converting to Slides: