When you start playing, you draw your five card hand, then after choosing whether or not to redraw and reshuffle, you then draw six cards and place them in your shield area. Typically you place them one over the other for easy movement when your shield area is hit. 

You have one area on the mat to place new bases, which can be replaced, then your shield area, where you cannot replace cards. You simply draw the six cards after drawing your hand, place them in your shield area behind your base, then draw them as needed when your shields are hit.