Remove the shelf and any parts from the refrigerator.
Wash the shelf and parts in the sink, removing any residual food stuck on the shelf.
Dry the shelf and all parts with a towel. Make sure the shelf parts are very dry to let the glue adhere most effectively.
Assemble the pieces on the counter before gluing to make sure you have everything you need and there isn't a gap in the broken area.
Line one edge of the broken shelf with the glue -- use a fair amount, but not too much.
Line the matching broken piece in place along the glue. Reattach the pieces by holding the pieces in position for a few minutes so the glue begins to dry.
Wipe away residual glue before it dries with the towel. Dampen it if you need to. Be careful not to move the alignment while cleaning excess glue.
Lay the shelf on a clean, flat surface to dry completely overnight before returning the shelf to the refrigerator.