What does it do? For brevity, we refer to these as 2dBVP plots. You may want to use these when you need to solve a boundary value problem, though it is not essential to do so.
How do I use it? When the display first appears, you should see the solution to the problem for the current set of boundary conditions, as well as two red objects at the boundary points of the domain. The red things are called ``beads'', and are provided to allow you to drag and drop boundary conditions using the mouse.
What are the defaults? The default display contains the rectangle (-10,10)x(-10,10). The display has a bounding box, shows axes labeled with tick marks by default, and shows trajectories and nullclines, if any. It does not show direction fields initially. The default boundary conditions are at (-10,0) and (10,0), unless you have already specified otherwise. The beads currently are always rectangles. You don't actually have to click on top of a bead to move it - it is sufficient to click near the bead.
This type of display appears by default when you type two differential equations (or a single second order one) in the equation dialog box, and check the BVP box before you close the equation dialog.