Hello, Sikha Thakur jee,
Welcome to the forums!
Artificial scarcity is scarcity caused artificially -- there may be different ways it can be caused in. It means the state of scarcity that is caused artificially, while hoarding refers to the most common way of causing artificial scarcity. (I don't think "artificial scarcity" is a term in dictionaries -- it's a phrase probably coined by economists.) "Hoarding" means the act of stocking money or things secretly so that other people are not able to use it. In economics, it often refers to the act of over-storing things to cause supply shortage so that the hoarder might make more money by selling products at a higher price when demand increases (because of short supply).
As I said, artificial scarcity is often caused by hoarding.
I hope it makes sense.
Note: You don't need any article before "artificial scarcity" there -- "scarcity" is an uncountable noun.