From the Allies perspective, there are 4 objectives to destroy on the map:
1) Field 88--this is the flak cannon on the left side of the map,
2)Radio Tower--the antenna in the front/middle of the map,
3)Cow 88--the flak cannon on the right side of the map,
4)Big Gun--the large cannon at the far back of the map.
From the beach you can see Left Bunker and Right Bunker. You have three avenues of attack, Right, Left and Mid. Taking the left path you will go past Left Bunker and Left Mortar Pit, through Field and to the Field 88. Continuing past the Field 88 you can go through Hole-In-The-Wall to the Trenches and even go through Big Gun Tunnels, passing through Steam Room, to attack Big Gun via Big Gun Ladder or Elevator.
If you blow Mid you get into the Trenches from which you can go left to attack the Sandbags from behind or go right to attack Radio Tower. You can continue to the right to flank Right Bunker or attack Cow 88.
If you go right you have to blow Sea Wall which gives you access to Right Bunker and Right Mortar Pit. Climbing up the ladder in Right Bunker and then climbing down the other ladder will take you to Dirt Tunnels after passing through Red Room. From Dirt Tunnels you can attack either Cow 88 or Big Gun.
Hope this helps!