Some example from Matsuo Basho:
the first cold shower [kireji]
even the monkey seems to want
a little coat of straw
After the first verse there is a change, like two sentences divided by the end of the first verse. We could put a period or a semicolon. In Japanese there are some words that do the same thing.
the wind of Fuji [kireji]
I've brought on my fan
a gift from Edo
spring going— [kireji, often marked with a hyphen]
birds crying and tears
in the eyes of fish
how cool the feeling
of a wall against the feet — [kireji]
siesta