If you don't know what's exactly called NFTs I strongly recommend you to read this blog 

Mintable.app

In this website artists can create NFTs for free.

Step 1: Go to mintable.app and click sign up

Step 2: Once you created your account, connect your Metamask wallet (If you don't have metamask wallet, click this Metamaskaccount and follow those steps to create your account)

Step 3: Link your wallet address with mintable ( You can see my Metamask wallet has zero balance )

Step 4: Click mint an item (Minting is the process of linking your art into block chain)

Step 5: Click create a new item

Step 6: Choose advanced to easy to create gasless minting

Step 7:  Click collectibles and create the eye catchy title and description. 

Step 8 : Add files

Step 9 : You can select either fixed price or auction with base price for limited time frame and click list this item

Step 10 : Click proceed 

Step 11: Click sign

Step 12: That's it. Your NFT is ready