if you mean who aggregates all of the coupon data for them, there are several parties that do it, and most are junk. the one premier service is an offshoot of a successful coupon site, who already was doing the work to aggregate the data for themselves. that one isn't cheap, but the data is rock solid. check them at formetocoupon.com.
if you meant you're a merchant and you're wondering how to get your coupons into couponshack, start an affiliate program at one of the popular affiliate networks (like ShareASale, CJ, etc) and tons of couponers will join your program and distribute the coupons you enter into the affiliate interface.