StartCorner (Enum/StartCorner) determines from which corner the grid starts laying out UI elements. The grid continues in the UIGridStyleLayout/FillDirection, filling elements one by one until UIGridLayout/FIllDirectionMaxCells cells have been laid out in that row/column or if all the parent UI element’s space has been occupied by previous cells.

Above, the potion is the first ImageLabel, followed by the gem and the sword. The UIGridLayout is using a Enum/StartCorner of BottomRight. The UIGridStyleLayout/FillDirection is Horizontal.