At the end of Ant-Man (2015), Michael Peña's character Luis delivers a typical rambling story to Scott Lang (Paul Rudd). The point of the story may be only that The Falcon was looking for Ant-Man, but Luis seems very pleased by the news and, given that Ant-Man and Falcon had been fighting earlier in the film, this seems an inappropriate reaction. I wonder if I missed something. What is the point of the story?
In-universe yes, it's to let Scott know that someone "who works with the Avengers" (We know to be Cap and Falcon, Scott may have figured it was Falcon) are looking for him. Luis, always the happy type, is attempting to hook his friend up with a job, same as he did earlier in the movie. To sum it up:
Luis: So I asked Ignacio, "Did the badass tell the stupid-fine writer chick to tell you to tell me, because I'm tight with Ant-Man, that he's looking for him?"
Scott: And? What'd he say?
Luis: He said, "Yes."
Out of universe, The scene is a simple Sequel Hook told through Luis' typical exuberant manner. As Luis says half way through the story when he goes on a tangent and Scott stops him,
Okay, sorry. Sorry. You know, I just get excited and stuff.
A Sequel Hook is something in a work that suggests that there is a clear possibility for another story. The MacGuffins may come in threes, the Big Bad might be Not Quite Dead, or, more blatantly, as the story ends another adventure might be shown beginning.
It's only there to setup the Post Credit Stinger, which itself is a Sequel Hook to Captain America: Civil War, or possibly even The Avengers 3: Infinity War, the overall end goal of the Marvel-Cinematic-Universe.
He's saying that Sam 'The Falcon' Wilson and Steve 'Captain America' Rogers are looking for help from Scott Lang.
We've known for a while now that Scott Lang would be making an appearance in Captain America: Civil War as part of 'Team Cap'. Luis' monologue here is him explaining to Scott that The Falcon is looking for him. Although Sam Wilson's motivations for looking for Scott at this point are somewhat ambiguous, a post-credits scene clears up the situation somewhat.
Set in some kind of warehouse, we see Sam 'The Falcon' Wilson and Steve 'Captain America' Rogers discussing what to do with James ' Bucky' Barnes (AKA The Winter Soldier) who has been trapped in some kind of vice. Steve and Sam have been searching for since the end of Captain America: The Winter Soldier.
From this answer;
Kevin Feige has said that the post-credits scene (technically the only one, as the other one is a mid-credits scene) was footage shot for Civil War and that the scene will appear as part of the larger final cut of Civil War in some way (the final cut still has to be edited).
"I won’t tell you exactly where it is, but that’s photography from Civil War. That is a part of the movie - it’s dailies from a part of the movie. Whether it will look exactly like that in the movie I think will shift a little bit, in terms of how we cut it, but that was footage shot for Civil War."
That answer also gives the following transcript of the post-credits scene in question. I have bolded the important lines.
Sam Wilson: This would have been much easier if it had happened a week ago.
Steve Rogers: We can't call Stark...
Sam Wilson: ...because he wouldn't believe us.
Steve Rogers: And even if he did...
Sam Wilson: ...the Accords might not let him help.
Steve Rogers: We're on our own here.
Sam Wilson: Maybe not... I know a guy.
I have my own theories on what "the Accords" are, but more importantly is the last two lines of dialogue. Steve thinks that this is an issue that he and Sam will have to sort out alone, but Sam "knows a guy".
From Scott's upcoming appearance on 'Team Cap' in Captain America: Civil War and Sam Wilson stating both that he is looking for Scott and that he knows someone who might be able to help, it is fairly clear that Sam is looking for help from Scott regarding the Bucky situation.