左边(zuǒ biān) - the left, the left-hand side in Mandarin

左边 (zuǒ biān) is the left-hand side. It belongs to the family of position words built with 边: 右边 (right), 旁边 (beside), 外边 (outside), 里边 (inside). In casual speech the 边 often drops to a neutral tone, zuǒ bian.

Chinese treats it as a noun, a place, not as a preposition. That is the whole grammar of it: the thing you are measuring from comes first with 的, then the position word. 路的左边 is the left of the road, 我左边 is my left, 照片左边 the left of the photo. With people and body parts the 的 is usually dropped.

The trap for an English speaker is reaching for a preposition. There is no word for "on" here; the job is done by 在 plus the position noun, as in 在左边. Saying anything like 在左边的路 flips the meaning into "the road on the left", which is a different claim about where the bank is.