First find a NFT you like... like this one:
or from the item page:
Check to make sure the information is correct!
Your transaction will be processed on the blockchain, within a few seconds you should see a new button to view the item in your profile, this means your good to go!
You can go see your items in your "My Orders" page on your profile. Once the transaction has been approved on the blockchain you can refresh the page and it will show "COMPLETED"