You hang it out behind a shed or garage, the lid has a little maze that they crawl into and then they can't find their way out.
My parents always used https://www.bigstinkyflytrap.com/ . It definitely caught a lot of flies, which can be different than catching enough flies of course.
It worked far too well.
Within a day it had attracted flies from a large surrounding area. The nearly filled jar of flies had a presence I can only describe as "Stephen King-esque" just buzzing with raw malevolence. If you think one large black fly can make quite the noise I invite you to listen to a 1000+ angry flies in a jar.
And while many were certainly capture - an equally abhorrent number were all over the cans and the side of the house. So a mixed experience.
I also tried once with an insecticide which also contained a bait, it came in granules and you had to mix with water and spray all over. The floor of my outdoors where full of dead flies.
Best advice I can give: never use any kind of bait. That’s completely BS, you are never going to kill them all. You want flies to go to another place, keep things clean.
Flies hate wind, use fans.
The method I devised to get rid of these large black flies from indoors:
Open a door and simply herd/walk them out by making yourself big. It's surprisingly easy - so much easier than trying to swat them. They seem to instinctively avoid things moving towards them, and because of that they're pretty easy to herd.