Adding your logo on the slides is done from the Design editor on the presentation. Move to the Design editor and click on the toolbox on the right edge of the screen.
Once the design options are displayed, scroll down a bit and find the Logo buttons. There's two square buttons to upload a logo for light and dark backgrounds.
A browse window will pop up for you to browse and upload your logo file. Make sure you have the image on the right size before uploading. The recommended file type is .png.
Once the file is uploaded, click on the Slide Options below the slide, to control the logo position on the slide.
The drop down menu will give you the options, including to hide it. The logo position is applied by default on all slides, and you can change it for specific slides according to your content arrangement.