Ah the Chorus. Can't live without it, can't quite figure out what it's doing. We want to first say that if you're still trying to wrap your mind around this half-character, half-not Chorus-thing, we're with you. And you know what? The Greeks, who invented the tragic Chorus, kind of are too. Choruses are famously mysterious and confusing; sometimes they seem to be full of wise words, and sometimes they seem totally nuts.
So, if the Chorus seem to be playing a lot of different roles at different times in Samson, then you're on the right track: it's their job.
But let's get down to details. This Chorus, like most Greek Choruses, has a specific identity: here they're a collection of Danites. The Danites were Samson's tribe of Israelites, so essentially, they're like a collection of his closest friends and extended family. (Just who you want showing up to "comfort" you, right?)
Unlike the other visitors Samson receives, the Danites stick around for the entire play and are often a kind of sounding board for Samson's own thoughts. While other characters arrive with some kind of agenda, something they seem to want Samson to do or agree to, the Chorus seem interested in just chilling with Samson and reflecting on the situation.
And they reflect in more ways than one. Let's take a look at something they say:
But see here comes thy reverend Sire/ With careful step, Locks white as doune,/ Old Manoa (327-9)
Here, the Chorus is telling Samson that his father is approaching. So, they help move the story along. But they also function as Samson's—and our—eyes. They see what he isn't able to, and they update him not only on things that are happening but on what they look like.
So, in a way, maybe we can think of the Chorus as a kind of an extension of Samson himself—thinking through his thoughts with him, and seeing what's going on.