From an interesting article about German http://www.dw.com/en/i-bims-german-youth-word-of-the-year-2017/a-41422471
First off - don't use it :)
The accent is on the (first, stand-alone) "i", which is long. "bims" is short.
What the article forgets to mention (edit: but gmbka did) is that it really means "it's me", not actually "I am": "i bims, 1 Maler" = "it's me, a painter".
"i" is dialect for "ich" in southern Germany / Austria / Switzerland. The correct spelling would be "ich bin's"* (short for "ich bin es").
I think the whole thing originated on a satirical Facebook page of "inspirational sayings with pictures", using intentionally bad spelling along with the bad sayings...
...and notably also using "1" for "ein(e)", and "vong ... her" = "von ... her" = "with regards to", "what with": "1 guter Maler vong Farben her" = "a good painter with regards to colours". Don't use "von ... her" in real life, please; it may be used in dialect at times, but it's not "good German" at all. It sounds awkward, like you don't know how to phrase things more elegantly. (It does shorten things, though, which is why I've been using it for decades before it was cool ;-) - "Das ist ein schönes Bild - von den Farben her." "That's a nice picture, what with the colours.")
The "Youth Word of the Year" is notorious for suggesting words the vast majority of the "youth" has never even heard of. In this case, people have heard of it, but many think it's ridiculous or, at any rate, outdated already. Some still use "i bims", "1", "vong ... her" etc. for funny/satirical Facebook comments when they want to sound daft.
*You can absolutely use "Ich bin's!" when you knock at a door. "Ich bin es" isn't used. If you recognise yourself on a picture, you'd say "Das bin ich!" instead.