If you’re in a state with an active, working exchange there’s no way to apply for a subsidy on healthcare.gov.
Well, I’m in a state with a state exchange and my description is how it worked.
To clarify, the state exchange was open and working, but the only thing we did there was see which insurers were available. The idea was originally to deal only with the insurer, but one could only get an estimate of the subsidy, from the insurer we chose. (It seems to me we did not find this on one of the other insurer’s sites, but maybe we did not look hard enough.) The insurer we chose sent one straight over to healthcare.gov (”hot link”) to apply for a subsidy if desired, after a policy was chosen.