vbvertice on Virtual Button sample

I wonder how the virtual button rendered on the screen?

why there's 96 vertices just to render 4 virtual button? 

yeah this particular code is really confuse me 

 

 // We add the vertices to a common array in order to have one single             // draw call. This is more efficient than having multiple glDrawArray calls            vbVertices[vbCounter   ]=vbRectangle->getLeftTopX();            vbVertices[vbCounter+ 1]=vbRectangle->getLeftTopY();            vbVertices[vbCounter+ 2]=0.0f;            vbVertices[vbCounter+ 3]=vbRectangle->getRightBottomX();            vbVertices[vbCounter+ 4]=vbRectangle->getLeftTopY();            vbVertices[vbCounter+ 5]=0.0f;            vbVertices[vbCounter+ 6]=vbRectangle->getRightBottomX();            vbVertices[vbCounter+ 7]=vbRectangle->getLeftTopY();            vbVertices[vbCounter+ 8]=0.0f;            vbVertices[vbCounter+ 9]=vbRectangle->getRightBottomX();            vbVertices[vbCounter+10]=vbRectangle->getRightBottomY();            vbVertices[vbCounter+11]=0.0f;            vbVertices[vbCounter+12]=vbRectangle->getRightBottomX();            vbVertices[vbCounter+13]=vbRectangle->getRightBottomY();            vbVertices[vbCounter+14]=0.0f;            vbVertices[vbCounter+15]=vbRectangle->getLeftTopX();            vbVertices[vbCounter+16]=vbRectangle->getRightBottomY();            vbVertices[vbCounter+17]=0.0f;            vbVertices[vbCounter+18]=vbRectangle->getLeftTopX();            vbVertices[vbCounter+19]=vbRectangle->getRightBottomY();            vbVertices[vbCounter+20]=0.0f;            vbVertices[vbCounter+21]=vbRectangle->getLeftTopX();            vbVertices[vbCounter+22]=vbRectangle->getLeftTopY();            vbVertices[vbCounter+23]=0.0f;            vbCounter+=24;

So I want to create my own virtual button from a trackables, but I don't know how to create and render it on screen just by looking at the sample. so If there's any clear step by step tutorial of how to create virtual button that would really help a lot.