I have been playing OpenRA for some months now on skirmish mode and last week I started in multiplayer games ( I'm really terrible but ok,

Before I started online games I have watched OpenRA multiplayer replays and watched the last big team tournament stream.
I have seen some things that I don't know how they do it, like my transport chopper always lands on the ground but I have seen that other players can let the transport choppers stay in the air, how do they do that? I can only do that if I send them over water or a mountain/building.
Also, another thing is that if I retreat my tanks they stop shooting, but I saw you can retreat with your tanks and they still shoot back. How do you do that?
The last thing is, I saw someone take 4 oil derricks with 1 command, like the engineer took the oil derricks almost automatic.
Great game, in the past I was addicted to red alert and it's coming back now XD
Hope my English is good enough to understand ^^