Usage patterns
〈物〉はどれですかwhich one is 〈物〉? (asking someone to pick out an item from several)
どれ、〈動詞〉well then, (let's) ~ (used to prompt oneself or others into action)
Well then, shall we get started?
どれにするto decide on which one (out of several) to choose
There are so many things on the menu, I can't decide which to have.
どれが一番〈形容詞〉かwhich one is the most ~ (of the options)
Which of these is the tastiest?
Expressions
どれだけhow much; how many; to what extent どれにもnone (of them); not any