How do I get the Paratroopers on to my Planes

You click the convert button that appears in their hotbar

I understand. I appreciate your help. When I convert the paratroopers to air units do they automatically board the plane when it takes off?

They become an aerial unit, as in their own plane. From there, you control them like a bomber just it spawns paratroopers.

Thank you for your help. I appreciate it.