Actually, there are rules for "that" and "which", but most English speakers don't know them. You would probably never be corrected if you mixed them up. However, it's always better to know, so...
"that" is used for an essential clause. In other words, if you need to identify a thing with the clause. "which" is used for non-essential clauses, when you have already identified the thing in the clause.
"The book that most typifies the modern novel is 'Moby Dick'"
"The book 'Moby Dick', which was written in the 1800's, typifies the modern novel"
In the first sentence, I used "that" because I had not identified the book, therefore it was essential. In the second sentence, I used "which" because I has identified the book, making it non-essential.
One more rule: If you use "that" in a clause, you can use "which" after, even if it is essential.
"That book, which was written in the 1800's, typifies the modern novel form."
One other rule: If you are refering to a person, always use "who". Use "that" or "which" when referring to groups or things.
One last warning: It is not necessary to know this in normal spoken English. As I said, very few of us native English speakers really know the rules.