Hre is a diagram https://www.google.com.ec/search?q=in+on+at&es_sm=93&tbm=isch&imgil=kWXYJ3kDTfJ8sM%253A%253B4Y6Hc8dq1XB15M%253Bhttp%25253A%25252F%25252Fenglishl09.blogspot.com%25252F2015%25252F02%25252Fwhen-do-we-use-in-on-at.html&source=iu&pf=m&fir=kWXYJ3kDTfJ8sM%253A%252C4Y6Hc8dq1XB15M%252C_&usg=__NQmeFxc6KWzIVuTpiPWTRfjX56M%3D&biw=1024&bih=431&ved=0CDMQyjc&ei=qy1WVd_kKLS1sQTFooGoDg#imgrc=kWXYJ3kDTfJ8sM%253A%3B4Y6Hc8dq1XB15M%3Bhttp%253A%252F%252F4.bp.blogspot.com%252F-P0Dcs3zYYyg%252FU2QUkmzivGI%252FAAAAAAAAACE%252F0dYIIPhYQE8%252Fs1600%252Fprepositions-real-life.png%3Bhttp%253A%252F%252Fenglishl09.blogspot.com%252F2015%252F02%252Fwhen-do-we-use-in-on-at.html%3B1318%3B860

ON - to express the surface of something: (e.g. "The book is on the desk.") - to specify days/dates: (e.g. "Let's meet on Wednesday." / "Let's meet on 23rd of April.") - to express someone using a device, or something in a device: (e.g. "She's on the phone right now." / "My favourite song is playing on the radio!") - to express a part of the body: (e.g. "He slapped me on my cheek.") - to express the state of something: (e.g. "The stove is on fire!" / "These clothes are on sale right now.") AT - To specify time: (e.g. "Let's meet at 4pm later.") - To indicate a place: (e.g. "He's at the hospital.") - To express an activity: (e.g. "He threw a ball at me." / "I'm not good at playing chess.") IN - To express unspecific time: (e.g. "He drinks coffee in the morning." / "The order will arrive in 2 weeks.") - To indicate a specific place or location: (e.g. "He's in the kitchen.") - To express a characteristic (shape/size/colour): (e.g. "We gathered in a circle." / "Does this shirt come in other sizes?" / "Does this shirt come in black?") - To express while doing something: (e.g. "In preparing for the exams, I stayed up all night to study.") - To express an opinion/interest/belief/feeling: (e.g. "I believe in you. You can make it!" / "I'm not interested in religion." From my answer to the same question by another user: http://www.italki.com/entry/534804 Hope this helps! ^_^

I like this simple and logical explanation for the prepositions of place in, at, on. http://www.youtube.com/watch?v=jLX9UqIo_kw Josie's link is great for the prepositions of time in, at, on.

I think prepositions are one of the hardest things to master when learning English. Some of my friends who are not native speakers have large vocabularies and little to no accent, but their use of prepositions is what gives them away. I think it is better to just get a feel for them than to get too bogged down with the rules. Maybe just type 20 or so sentences the way you think they should be and then post them on this site to be corrected. Make note of your errors and try again. The problem with just practicing speaking English with others, is that they often will not correct mistakes with prepositions because they'll be able to understand what your saying even with the errors.

The hard is remember all this rules. Almost impossible.