How do I send my plane to connected players?

I can’t find detailed explanation how to send my plane to connected players

After handling my plane, I can choose where I’ll send it
For example, if I wanna send my plane to Prague connected user, all I have to do is just choosing Prague airport: is that right?

Yup. That’s it really

What about all the airports that are not playable, but are listed, what happens then?

You have to do the same thing but if the destination is green You have not unlocked it yet. To unlock it You can go to the connections tab.