I think the answer is
The word "what"
You put it in your mouth to use it, but you can't eat it or taste it.
You voice the word "what" to use it but the word has no specific taste.
People often point when they use it, but you can't see it or touch it.
If they are about to say "What is that?", for example, then a person may point to the object in question.
Everyone knows how to use it, but you only use it when you don't know what it is.
Everyone knows how to ask a "what" question and it's generally only used when you don't know to what the "what" is referring.
What's the word I'm thinking of