There is one Axis chart divided into two sections. Half the chart comes in on the St. Lo side of the board or the sections in the middle and one half comes in on the Caen or sections in the middle. I don’t have the board in front of me. Certain sections of the board can have units brought in from either half of the chart.
When the order card comes up to roll for re-inforcements you roll two six sided dice for each side of the chart. Bring the resulting numbers of units off the charts. Top to bottom and left to right. The units must be brought on in order. Also they are shot at by aircraft individually. You do not put say 7 units in a box and roll 7 aircraft dice and just kill INF.
For the British chart and the US charts you roll two six sided dice for each chart. However in the Allies case the units have certain beach restrictions near the top of the chart. If the boxes out in the ocean representing ships at sea are full and the units that are next on the chart must come in at that beach then you will have to wait until you clear the boxes and the next re-inforcement phase comes up to bring those troops onto the board. Sometimes you lose out bringing stuff in because of congestion in your zones/beaches.
Hope that helps.