Q. What should I know if I'm going to use Google Slides instead of Keynote/PowerPoint?
There are lots of great reason to use Google Slides over Keynote or PowerPoint, especially if you want to work on the slides with other people, or/and if you want others to be able to view your slides without emailing them a massive attachment, they may not even be able to view if they don't have the right software/computer.
But there are a couple of downsides...
Google Slides can handle video, but you have to have a reliable internet connection while you are presenting, and the video you want to use needs to be in YouTube or in your Google Drive/Photos. You can't change how the video is displayed other than the size, that's it. With the others you can drag and drop a video in, and even adjust the parameters, ie mute the sound, have it automatically start/stop at certain points, change the image that displays before you play the video...
Google Slides and Presenter notes are fiddly, but it's not insurmountable. This is where you want your main presentation to appear on one screen (via a projector) and your notes, and the control of the presentation to appear on another (your laptop screen). Keynote and PPT are built to automatically display this way, unless you override it. With Google Slides you have to set it up manually, here's how.
Arguable the simplest solution is to download the Google Slides as a PowerPoint presentation, then just use Keynote or PowerPoint for the presentation, there may be some formatting changes to make though...
The proper way:
Connect to a second screen, eg via a projector
Make sure the second screen is not mirrored—that it is usable as a second screen (command + F1 on a Mac)
Open the presentation in Google Slides, not full screen.
In the top right corner, next to "Present," click the Down arrow .
Click Presenter view.
Click Speaker notes.
"Show speaker notes" will open up a new window.
Move that Speakers Notes window to the other screen on your laptop and have the presentation playing full-screen on the external monitor.
Now you can see your notes and control the presentation from the privacy of your laptop screen.