This toolbox can be opened via the Window > Standard Toolboxes menu.
This toolbox is intended for use with 3D layers, in order to create a 2D cross-section of 3D object.
Use 3D - New - Grid to create a grid and position it so that the Cross-Section toolbox displays the outline you require.
Create - click to create a new one-up layer and place the cross-section geometry within it, or use the pull-down list to choose an existing 2D layer into which the geometry is to be created.
Extents - click to create geometry matching the current grid extents (width & height).
Width & Height - can be used to alter the size of the grid (if required).
Cross-Section Standard Toolbox
Related topics: Notes On 3D Tools, Notes On Standard Toolboxes.