question about english grammar?

In general, we see "in" as being contained by borders, wall, limits, a period, etc. (both literal and metaphoric). With "at" we generally imagine a point in space or time. Then we have fixed expressions like: at home at the office at (the) school at play at war An example would be: "Rookiekan is in the house." We know from this sentence that Samand is inside the house. "Rookiekan is at the house." We cannot tell from this sentence if Rookiekan is inside the house or outside the house but we know he is somewhere at the house. Today I was at the office. If someone phoned at my home asking where I was they would have been told "Mummy is at the office." While I was there if someone was looking for me, they would have asked where is Mummy? For most of the day the response would have been; "She is in her office." I have a room in a building that is my office, however during the day I move to and from my room to interact throughout the building, the whole place where I work can be refered to as "the office" in which case you would say 'at' but when I am actually within my office you would say 'in'. Are you more confused now? I think I am. Right now I am sitting at my desk infront of my computer in my office at home. LOL!

At a place just means your there like "I just pulled at McDonalds". In a place suggests that your not just there but your actually in the building or whatever. "I am in Mcdonalds" One suggest your just there on the outside and one is your in.