Help with Loot Table Commands

Hello,

I need help with loot table commands. I've tried YouTube videos and other posts on the forum, but every time I try the command out it is either is invalid or in the chat it says changed block data of cords, but every time the chest is empty.And just to make sure its incorrect ,I press control+mmb and each time get no chest. Maybe I'm doing it wrong, but I need help. I have tried for three days already.