What problems did American troops face once they arrived in France?
I assume you are speaking of the World War II invasion of Normandy. Since the invasion was by sea, the initial attacks met with fierce resistance from German land forces. In some areas, the beaches held high points (such as the infamous Pointe du Hoc) that were well defended. The Germans laid many obstacles in the water and on the beach. Once the Allied forces secured the beaches, they had to deal with land mines that were left behind by the retreating Germans. Air attacks by the Luftwaffe were constant, though the Allies eventually gained air superiority. The hedgerows found in the country also proved to be impenetrable. Food was scarce, since the Germans had taken most of what was available with them. Needless to say, the language barrier also proved to cause some problems as well.
Perhaps the most important problem that the American troops faced when they first arrived in France was that they had no idea what they were doing. Most of them had hardly had any training and so they were not really ready for combat.
Another problem you could mention was that the British and French armies wanted to break up the American armies. They wanted the Americans to be put piecemeal into British and French formations. The American commanders thought this would be a really bad idea for American morale. They also thought the Americnas would be used as cannon fodder.
Finally, you could talk about the particular problems of black troops. They faced discrimination, but really only from their fellow Americans -- they were more of a novelty to the French.