Command Breakdown
/give - gives the player the item
@p - runs command for the nearest player (Probably you)
(diamond_pickaxe) 1 0 - replace the bracketed word(s) to select the item make sure to put an underscore instead of a space
{CanDestroy: - The modifier that allows this tool to break a certain block in adventure mode
["YourBlockHere"]} - change YourBlockHere to another block such as grass or diamond_ore make sure to put an underscore instead of a spacePlease comment if any mistakes were made