I have bought Minecraft on iPad and looking to use on my Mac air however when logging it it advises I have no license? please advise.

i have minecraft on my ipad and working successfully, however looking to use on my macbook air.   i have downloaded the app from the website however asking me to re-purchase although put in my email and password.

can you please advise how i do this and the steps to transfer me world on the mac?  i have the files from the ipad from the files but unsure where to put them.