Hi,

2 ways to map a sidewalk. 1) if physically separated, a raised curb e.g., draw a way parallel to the road at side(s) where they are. make sure to connect at every crossing of other way. If part of the road, e.g. when just marked by a painted line, a colored surface with symbols like we have here often, mark the road with sidewalk:left/right/both=lane. (left is viewed from the direction the way was drawn).
Questions, ask at the community forum: https://community.openstreetmap.org/categories

ciao