Think "in" for inside, "on" for on top of: - I'm in(side) my house. - I'm on (top of) my roof You use "at" if you are describing that you are currently "at" a place: - I'm at the store. - I'm at my grandmother's house. "At" is more of a general preposition. It doesn't give you much of a picture in your head. You can use other prepositions to clearly communicate where you are. Here is a list I found... http://www.englishclub.com/grammar/prepositions-list.htm "The" is different because it is an article (the grammatical term for it). It is most similar to "a" and "an". You use "the" before nouns and adjectives: - The water. - The hot water. - The table. The difference between "a" and "the" is that "the" makes the noun more specific or special. - This is not just A skirt, it is THE skirt! So if you are talking about one specific item, you definitely use "the" and if you are talking about a type of item use "a" or "an". - I wanted a car but the car I saw was in need of repair. It is pretty easy to recognize when to use "a" and "an". "An" is only used in front of words that start with vowels, so... A... - car - skirt - website An... - airplane - idea - example An exeption (see what I did there?) to this rule is some words that start with H. Some of them have silent H's so they also use "an", like... An... Honor/honour [American spelling/Canadian & British spelling] Honest (person, thing) Herbal (thing, like tea) Well I think that's it! :)

Thami you use the word "in" as this example: I sat in the tub for an hour. I was at a friend's house all day. I sat on the fence. The cat is in the window. (the word "the" is usually followed by a noun). I hope this helps. If you have any other questions let me know.