Great question, glad you asked. A detail is a group of soldiers assigned to a specific task (eg, picking up litter), whereas a Squad is a sub-unit led by a NCO and subordinate to a Platoon (in the British Army we tend to call this a 'Section'). Hope that helps.
Incidentally, we don't march in boxes as it can get claustrophobic and requires ventilation and lighting. Much better to use a drill square or similar.
gunner, i understand that and all ready knew that. I was meaning when taking drill the precautionary word of command. If you are only drilling say 4 people is it still squad? I thought if it was less that 9 it was detail.