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