Preposições

Prepositions are short words (on, in, to) that usually stand in front of nouns (sometimes also in front of gerund verbs).
Even advanced learners of English find prepositions difficult, as a 1:1 translation is usually not possible. One preposition in your native language might have several translations depending on the situation.
There are hardly any rules as to when to use which preposition. The only way to learn prepositions is looking them up in a dictionary, reading a lot in English (literature) and learning useful phrases off by heart (study tips).
The following table contains rules for some of the most frequently used prepositions in English:
Prepositions – Time
English Usage Example
 on  days of the week  on Monday
 in  months / seasons
 time of day
 year
 after a certain period of time (when?)  in August / in winter
 in the morning
 in 2006
 in an hour
 at  for night
 for weekend
 a certain point of time (when?)  at night
 at the weekend
 at half past nine
 since  from a certain point of time (past till now)  since 1980
 for  over a certain period of time (past till now)  for 2 years
 ago  a certain time in the past  2 years ago
 before  earlier than a certain point of time  before 2004
 to  telling the time  ten to six (5:50)
 past  telling the time  ten past six (6:10)
 to / till / until  marking the beginning and end of a period of time  from Monday to/till Friday
 till / until  in the sense of how long something is going to last  He is on holiday until Friday.
 by  in the sense of at the latest
 up to a certain time  I will be back by 6 o’clock.
 By 11 o'clock, I had read five pages.
Prepositions – Place (Position and Direction)
English Usage Example
 in  room, building, street, town, country
 book, paper etc.
 car, taxi
 picture, world  in the kitchen, in London
 in the book
 in the car, in a taxi
 in the picture, in the world
 at  meaning next to, by an