Can you help me understand "Law of Conservation of Matter and Energy”?

I was reading a little bit of the “Law of Conservation of Matter and Energy”

which says basically nothing can be created or destroyed…..in which point I looked around the room, my bed, computer what not , if this was made then indeed it had been there before? All we have done is taken what was there and changed it into something else.

But its still the same amount its all there.

If something like this is true then I cannot create or destroy then how are we ever alive or dead, if I were to never be created then how can I be killed?

Since in truth I had to by made from what existed , a transfer of energy and matter but not truly “made” for me to be new.

In a sense if I added more energy or mass, the world could implode like a overfilled air tank?

So before I lose my mind, anyone mind explaining this to me more?

I am simply going of what they are saying and trying to put it together.

Thank you.