I'm lying on my bed, which is in my bedroom, and I'm looking at my laptop. (Which is at the end of my bed). I see a very pretty English student. God bless Mexico. :p

Mustafa gave a great explanation. I'll just give some more examples: Examples: -If I'm on a building, I'm standing on the roof (or climbing the walls!). -If I'm in a building, I've walked inside and am in a room. -If I'm on a planet, I'm standing on the planet. -If I'm in the planet, I'm deep underground! -A clock is on a wall. -Termites live in the wall. -Grass grows on the ground. -Ants live in the ground. -A show is on television (imagine it attached like a poster). -Wires are in the TV. -Birds sit on cars. -People sit in cars. 'At' is just a general word used to describe where something is located. If none of the other prepositions apply, it's usually safe to use 'at'.

In general, at for a POINT in for an ENCLOSED SPACE on for a SURFACE at in on POINT ENCLOSED SPACE SURFACE at the corner in the garden on the wall at the bus stop in London on the ceiling at the door in France on the door at the top of the page in a box on the cover at the end of the road in my pocket on the floor at the entrance in my wallet on the carpet at the crossroads in a building on the menu at the front desk in a car on a page Look at these examples: Jane is waiting for you at the bus stop. The shop is at the end of the street. My plane stopped at Dubai and Hanoi and arrived in Bangkok two hours late. When will you arrive at the office? Do you work in an office? I have a meeting in New York. Do you live in Japan? Jupiter is in the Solar System. The author's name is on the cover of the book. There are no prices on this menu. You are standing on my foot. There was a "no smoking" sign on the wall. I live on the 7th floor at 21 Oxford Street in London.