Combat in Rift is similar to most MMORPGs. Players have to target an enemy and then select abilities from their hotbars. However, Rift will feature a global cooldown which triggers after any skill or ability is used as shown in the latest GameTrailers video.
Many spells are linked to a global cooldown, this means that you can only cast one spell at most once per second.
You can queue a spell up to half a second before the current spell completes, this is stored server side and the queued spell will happen as soon as it can with the combat rules.