How to recognize?

[Amy]

When do I need to use 'at'?
Why musn't i use 'at' in this sentence?
I put some towels at the bathroom.
Why is this sentence correct?
I put some towels in the bathroom.

[Mister Micawber]

'At' is a point position-- it has no dimensions, so to speak.
'In' is a location within, enclosed by, inside something else.

I bought some towels at the department store (it is far away, and I am just speaking of its point location in space; I am not thinking about its interior, as of course I did not buy the towels outside the store) and I put them in (or into) the bathroom (that is, within that room rather than leaving them on the kitchen table or outside the bathroom door).

[Casiopea]

When do I need to use 'at'?
Why musn't i use 'at' in this sentence?
I put some towels at the bathroom.
Why is this sentence correct?
I put some towels in the bathroom.

'in' is short for inside, so when I say, "I'm in the store", I am expressing that I am inside the store.

'at' refers to a general location, so when I say, "I'm at the store", I am expressing that I could be in the store or outside the store. 'at' is a great preposition! Unlike 'in', which tells people exactly where you or something is located, 'at' is vague. It refers to a general location.

Use 'at' to talk about a general location, and use 'in' to talk about inside the location.

I put the towels at the bathroom. (Not OK)
I'm standing at the bathroom door. (OK)

I could be inside the bathroom standing in front of the door or I could be outside the bathroom standing in front of the door. Both meanings are possible with 'at'. It's a great preposition.

[Steven D]

When do I need to use 'at'?
Why musn't i use 'at' in this sentence?
I put some towels at the bathroom.
Why is this sentence correct?
I put some towels in the bathroom.

Use "in" for enclosed areas or for spaces with limitations.

A bathroom is an enclosed area, so we say "in the bathroom".

space with a limitation - They're in the water. (at the beach) We might consider that the ocean is not an enclosed area, but a space with a limitation.

The satellite is in outerspace. - Once again, "outer space" is not an enclosed area, but it does have limitations.

Use "at" for locations. I bought some paper towels at the store to put in the bathroom.

Where's Joe? He's at the store. - The speaker and listener can't see the store. They are relatively far away from it.

Where's Joe? He's in the store. - The speaker and listener can see the store. They are most likely in the parking lot of the store or very close to the store.

[Amy]

Thanks
I got it

[Casiopea]

That's Great.