Prepositions allow the writer to establish relationships between things and actions. They indicate origins, destinations, possession, recipients, time, etc.
Common French prepositions are presented in the following table:
When the prepositions à and de precede the determiners le and les, the result is a combined form:
To mean "to" or "in", French uses à, au, à la, en or dans le/la, depending on the kind of location. French indicates "from" by de, du or d', again depending on kind of location. This is illustrated in the following table:
The words pendant, dans, en, pour and depuis are used to indicate when an action started or how long it lasted. Let's consider each of these in turn:
Pendant:
Dans:
En:
Pour:
Depuis:
In both English in French some verbs are followed by a preposition (à or de in French), while others are not. The most common verbs are presented in the following tables:
Je joue aux cartes (note that this takes de when followed by a musical instrument).
Note that s'intéresser is followed by à, NOT dans; when jouer à is followed by a determiner, a contracted form is used, e.g.: je joue au baseball.
Pay particular attention to the verbs that are followed by de in French, but by "to" in English (e.g.: décider, essayer, oublier, menacer, etc.)
More information on anglicisms can be found here.