When a chicken comes up against a snake they will try to ward it off and sometimes they will be successful in scaring off the snake.
But sometimes larger snakes such as a boa or python snake may be able to actually just swallow the chicken or attack it even though the snake is trying to defend itself.
Chickens and baby chicks as well as the chicken eggs are prey for most snakes so you should do what you can to keep the snakes away from your chickens and the chicken coop.
Just having chickens though doesn't mean you'll have a problem with snakes but sometimes you might get some snakes trying to get to your chickens.
To keep snakes and rodents away from your chickens and chicken coop store your chicken feed in rodent-proof containers, and also consider a treadle feeder that the chickens have to step on to access food.
Also make sure to keep areas around the coop clear and free of hiding spots for snakes and keep grass and bushes well trimmed.
Remove dead leaves and brush piles and keep the outdoor area and outdoor run clear.
Doing all those things can help keep snakes and rodents away from your chicken coop and your chickens.