It is non-standard English; however, it is used quite a bit especially when someone wishes to give the impression of being relaxed in his speech or to indicate a lack of education. "Ain't" might have originated as a contraction of "Am I not"; however, these days it's used for every subject pronoun and even as a replacement for ""to have" in the perfect tenses. I ain't ready. (I'm not ready.) They ain't crazy enough to do it. (They aren't crazy enough...) Ain't you listening? (Aren't you listening?) Also in: He ain't been there. (He hasn't been there.) I ain't opened the door yet. (I haven't opened the door yet.) Be aware, however, that it is VERY informal speech and denotes a less-educated speaker. As an English-learner, you might not want to use it.

The word "ain't" is highly regarded as word used by little educated people, it basically means "aren't" or "isn't" as in "He ain't what I thought, dawg" or just a random and unnecessary negative contraction used in sentences like "ain't nobody got time for that", although I do feel it has some kind of emphasis here, but please, don't take my answer as final, English ain't my mother language

ain't meaning have not or has not. or am not / is not / are not Although widely disapproved as nonstandard and more common in the habitual speech of the less educated, ain't in senses 1 and 2 is flourishing in American English. It is used in both speech and writing to catch attention and to gain emphasis <the wackiness of movies, once so deliciously amusing, ain't funny anymore — Richard Schickel> . It is used especially in journalistic prose as part of a consistently informal style <the creative process ain't easy — Mike Royko>. This informal ain't is commonly distinguished from habitual ain't by its frequent occurrence in fixed constructions and phrases <well—class it ain't — Cleveland Amory> <for money? say it ain't so, Jimmy! — Andy Rooney> <you ain't seen nothing yet> <that ain't hay> <two out of three ain't bad> <if it ain't broke, don't fix it>. In fiction ain't is used for purposes of characterization; in familiar correspondence it tends to be the mark of a warm personal friendship. It is also used for metrical reasons in popular songs <Ain't She Sweet> <It Ain't Necessarily So>. Our evidence shows British use to be much the same as American. Copied :)