You can jump 2 inf from any friendly Airbase per turn, but you can’t do exclusively para attacks, other land units must be present. This prevents Russia in particular from having to do deep defenses when it can’t afford to.
If the para is joining an amphibious assault, it cannot retreat (just like other land units). If it is not an amphibious assault, it can retreat with the rest of the attacking units.
If you are attacking a space with AA guns, always send paras, even if it is an adjacent land territory. AA fires at paras and you can pick your 3ipc infantry as AA hits instead of planes. The more aibases you have, the more paras you can send. Really frustrating for the defender. I’m not a fan of these rules, and for a while it seemed like they mike get tweaked, but it didn’t happen.
I’d like to see a limit applied to them per turn for each power. Perhaps 2 per turn, per theatre.
I hope that explanation helped.