So French relative pronouns are pronouns that link two clauses together. In English we use 'who', 'whom', 'which', 'that', etc..
There are a bunch of relative pronouns in French but the basic ones you should know are: 'qui', 'que' and 'dont'. I'll give you a brief explanation and give you a some examples for each one.
- Qui is used when you're dealing with the subject
E.g. 'The man knows me. He is funny.'
'L'homme me connaît. Il est drôle.'
If you wanted to link these two clauses you would say:
'The man who knows me is funny.'
'L'homme qui me connaît est drôle.'
Another example:
'The book is old. It is interesting.'
'Le livre est vieux. C'est intéressant.'
Linking these two would become:
'The book that is old is interesting.'
'Le livre qui est vieux est intéressant.'
- Que is used when you're dealing with the object.
An example:
'I read the book. It is interesting'
'J'ai lu le livre. C'est intéressant.'
Linking these two but puting 'the book' first would turn into:
'The book that I read is interesting'
Here, you would use 'que' rather than 'qui' because 'the book' is the object of the verb 'read.
'Le livre QUE j'ai lu est intéressant.'
Dont is used when you're dealing with the object of 'de'
Example:
'J'ai beson du livre. C'est cher.'
'I need the book. It's expensive.'
Using relative pronouns to link them would turn into:
'Le livre dont j'ai besoin est cher.'
'The book that I need is expensive.
You would use dont here because 'le livre' is the object of 'besoin de'
Another example:
'Il a rêvé d'une fille. Elle était belle.'
'La fille dont il a rêvée était belle.'
There are many more relative pronouns such as: lequel, auquel, duquel, ce que but the ones I gave you are the most common ones you'll encounter.
Here's an article that gives more detail and will probably explain it better than I did:
http://french.about.com/od/grammar/a/relativepronouns.htm