Here are the commonest uses of these prepositions: TIME in the morning/afternoon/evening in January/February etc in summer/winter/autumn/spring in 2012 in the 20th century on Monday/Tuesday etc on Monday morning/Tuesday afternoon etc on my birthday at night/at the weekend/ at Christmas (NB this varies according to whether you use GB or US English) PLACE The whisky is in the glass The glass is on the table. in New York in Colombia in Europe 'At' is used for locations where you are interested in the function of the place, rather than the idea of physically 'inside' the place. At home/work/school There are also hundreds of other expressions eg 'on my way' which you just have to learn. DON'T try to translate these words directly from Spanish - you should note how English speakers use these words and then copy and learn them. Good luck

Here is a website that talks specifically about these three prepositions. http://www.talkenglish.com/Grammar/prepositions-on-at-in.aspx Hope this helps!