These disarmingly small little fellows actually cause a disproportionate amount of havoc in languages, not only in Italian. And I'll tell you why.
You can't just learn these as vocabulary items and be done with it. Oh no. In other words, it isn't enough to say that di means "of," da means "from," con means "with," and so on. Language (and life) is not like that.
What happens is that the usage of prepositions is thoroughly idiomatic, which means that translating literally isn't going to do it for you. In fact you'll be in a heap of trouble. Let's look at some examples (as always).
Viene da Pistoia. He's from Pistoia.
Literal, straightforward, easy.
But:
Vado da mio fratello. I'm going to my brother's (place).
Here, da is rendered by the English preposition "to."
Sono nato a Milano. I was born in Milan.
The preposition a is rendered by English "in."
But:
Sono nato in Italia. I was born in Italy.
Vivo con mia madre. I live with my mother.
But:
E' sposata con un medico. She's married to a doctor.
This sort of thing happens all the time, and there isn't a damn thing you can do about it. Not only that; sometimes Italians use a preposition where we don't, and vice-versa.
Ho comprato dieci tazze da caffe'.
I bought ten coffee cups.
Vado a casa.
I'm going home.
How are you going to know what to do? When it's idiomatic, you simply won't. You'll have to memorize usage on a case-by-case basis, although there are some broad general rules on the use of each preposition. You'll find these in a good grammar book.
As if this wasn't bad enough, you have to use the compound form when the article is required. Thus, you will have to remember the appropriate preposition, appropriate article, and the right compound.
Lavora nel Venezuela. He works in Venezuela.
nel=in + il (Venezuela is masculine)
What this means in practice is that the flawless mastery of prepositions will be one of the very last things you achieve in Italian. Even advanced speakers mess up.
For a long but still incomplete list of these troublesome prepositional uses, look here.
