Move Keynote presentation from Mac to iPad/iPhone
iCloud Drive

If your iOS devices are using iOS 11 or above, then the easiest option is to just save the Keynote presentations to your iCloud Drive. Your iOS device will be able to access them from the Files app and launch Keynote to view them. Likewise, you can launch Keynote first and then browse to your iCloud Drive to access them.

iTunes

Another option if your device is running iOS 10 or earlier, is to just use iTunes on your Mac to transfer your presentations. This option may also be quicker if you have large presentations or lots of them, as the transfer happens via USB cable rather than the internet.

To transfer via iTunes, follow these steps:


Launch iTunes on your Mac
Connect your iPhone/iPad to your Mac via USB cable
After a short while you'll see an icon appear that represents your iOS device - this should appear to the right of the drop-down menu (near top left of the iTunes window)
Click on the icon to view your device's summary screen
In the left-hand pane of your iTunes window you'll see various options for your device (e.g. Summary, Music, Movies, and so on)
Click on the File Sharing option (it should be the last one)
Now you'll see the File Sharing screen appear on the right-hand side of your iTunes window. This screen will list all the iOS apps that support file sharing.
Click on the Keynote app
On the right you'll now see a list of Keynote documents saved within this app on your device (assuming you already have some)
If you scroll down to the bottom you'll see an Add... button at bottom-right
Click on this button and use the window that appears to navigate to and select your Keynote presentations
Click on the Add... button 
Now your Keynote presentations are transferred to the device
When finished, click on Done button 


Now when you open Keynote on your iOS device and select the Browse option, you'll see the presentations listed there.

Note: This method is also available in iOS 11.