How do I make knives do damage?

How do I make knives do damage and throw knives?

There is no single way to make something do damage, just as there is not only one way to track health, and just as there are so many ways of describing shapes, players, and weapons in terms of their various geometries.

Before you ask the questions "How do I make knives do damage?" and "How do I throw knives?" you need to ask yourself some questions about your understanding of programming, mathematics, and solving these sorts of problems. Do you know anything about scripting at all? Are you familiar with the ROBLOX APIs by browsing the official wiki? Can you break this question down into smaller questions? For us to answer this question according to your needs, you have to give us a sense of how much you already know about what you are trying to achieve.

You can't expect us to write a "For Dummies" tutorial that covers every single aspect of what you are trying to achieve, nor should you expect us to know already what 'level' you are at. That would be requiring us to write redundant information and waste our time.

I'd ask that you give some more background details, ask a more specific question, and furthermore (depending on your experience) I would recommend starting with something simpler. The question you pose can be decomposed into lots of smaller problems.

The best way to learn is to practice. Start with attempting some smaller things, experiment a lot, be patient, and only post to the forums when you are at your wit's end - when you have exhausted all possible ideas that you can muster. For some problems that you may encounter in your scripting journey, this includes talking with your friends, maybe your parents, school teachers, and making use of the forums as a resource and not as your personal workforce.