Some players offer to trade spawners for cubits, there's no official way to "trade" cubits, like with /ah, but to give cubits you do /cubits pay <IGN> <Amount>. When players offer to trade, they mean they're looking for someone who's buying/selling something for cubits, such as spawners.
The typical rate for spawners is; 1 spawner = 0.01 cubits (2,000 mana).