Each encounter power you have can be used, normally, once, save for healing word.
Healing word notes:
Special: You can use this power twice per encounter, but only once per round.
Therefore, as a half-elven cleric (I'm skipping human for now), you get your racial encounter power usable once (until you can take a short rest), your cleric's level 1 encounter power usable once (until you can take a short rest), your cleric's channel divinity (ibid), and your healing word (usable twice, because it says so.)