It is an adjective.
Meaning: striking against something with a jolt.It is also used to refer to something disagreeable to the sense of hearing i.e when something had caused a harsh and irritating sound which is unpleasant to hear.
Synonyms : clashing, conflicting, contrasting, incompatible, incongruous, discordant, dissonant, inharmonious,bumpy,jolty,scratchy,squawky,
Antonyms : harmonious, pleasing,agrreable
1)The room was tastefully decorated except for the dark coloured curtains which had a jarring effect on the rest of the decor.
2)The jarring noise of the iron gate scraping on the ground had become a nuisance to us.
3)The continous talking jarred on my nerves.