how do I transfer photos from my macbook air to my ipad?

Use iTunes to Sync photos: Sync your iPhone, iPad, or iPod using iTunes on your computer - Apple Support

This article gives you a number of options.

How to transfer photos to an iPad

https://www.macworld.co.uk/how-to/ipad/transfer-photos-ipad-3504873

I would recommend that you use the iTunes sync method. You create albums on your Mac using the Photos app.

You can then synchronize those photo albums to your iPad and all of your iOS devices.

Howard