@Tink1113 @andrew
Not a big difference between “that” and “which”; it’s basically up to you which one to use. They’re both relative pronouns in that they relate to another noun in a sentence. However, “which” is often placed before a comma. The only difference people will say is that “that” is often used with essential information:
The cat that belonged to Marian was always getting lost.
It’s up to the writer to decide that you must know that the cat belongs to Marian. In that case, the word “that” is used because the information about whom it belongs to is essential.
The cat, which was Marian’s, was always getting lost.
In this case, “which was Marian’s” is separated by commas and is not necessarily important information and could be left out of the sentence.
Still, there isn’t really a “rule” for it; it’s up to you.
Also, the word “that” has four uses. One as a demonstrative pronoun as in ”that is my cat”, one as a demonstrative adjective like ”that cat is mine”, one as a relative pronoun like “the cat that belonged to me was the best”, and one as a conjunction like “it was obvious that the cat hated me”. The latter can be omitted sometimes; you can just say “it was obvious the cat hated me”.