WHO for people
The man who showed me the way was very polite.
WHICH for animal and things
My new guitar, which I bought yesterday, is excellent.
THAT for people but in a less specific way
The people that go out to riot are taking huge risks.
THAT in combination with a superlative
That is the best cup of tea I have ever had.
THAT if these words are in the sentence: all, any, anything, everything, first, last, nothing, only, something.
There is nothing that I like in this store.